Arab Journal of Nuclear Science and Applications, 94 (3 ), ( ) 2016

Transcription

1 CYANEX Reagents as Potential Extractants for Valuable and Hazardous Elements from Different Aqueous media J.A. Daoud Hot Laboratories and Waste Management Center, Atomic Energy Authority, Egypt Received: 5/1/2016 Accepted: 20/2/2016 ABSTRACT 1 The possible use of the different commercial organohosphorus reagents of the CYANEX series for the extraction of valuable and hazardous elements is explored. The potential advantages of each of the CYANEX extractants over other extractants are exploited in terms of higher loading capacity, selectivity, equilibration time and reagent concentration. Rare earths, uranium, thorium, palladium, cadmium, lead, copper, zinc, cobalt, nickel and chromium are among the elements extracted by CYANEX reagents from nitrate, phosphate, sulphate, chloride, thiocyanate as well as mixed media. The use of different techniques for the extraction processes by CYANEX reagents as conventional liquid-liquid extraction, continuous countercurrent extraction, Lewis cell and liquid membranes technology are presented. The efficiency of these extractants and the viability of the proposed systems for the selective extraction and separation of these elements from real and simulated waste solutions and from their ores is also discussed. Keywords: CYANEX Reagents; Liquid-Liquid Extraction; Rare Earths; Heavy Metals; Membranes; Palladium; Uranium; Thorium; Beryllium. 1. INTRODUCTION CYANEX reagents which are commercial organophosphorus extractants have been widely used in the treatment of radioactive waste solutions (1,2). In this respect, CYANEX 301 was used for Am/Eu separation from high active waste (HAW) (1). CYANEX 272 has found wide applications as individual extractant or in the synergistic mixture in treatment of radioactive waste (3-8). Daoud et al. (9) used CYANEX 272, CYANEX 301 and CYANEX 302 for the extraction of U(IV), U(VI) and Th(IV) from nitric acid medium and reported that CYANEX 272 is preferred for the extraction of U(IV) and U(VI) while CYANEX 302 gives high Th(IV) extraction. The same authors (10) used these three reagents for the extraction of Zr(IV) and found that the maximum extraction of Zr(IV) from 3M nitric acid increases in the sequence CYANEX 301< CYANEX 302 < CYANEX 272. The extraction of U(VI), Nd(III), Fe(III) and Co(II) by CYANEX 301 in kerosene revealed that this extractant is efficient for the extraction of uranium, cobalt and iron from 0.1M aqueous nitrate solution while it did not extract neodymium under the investigated conditions (11). The mechanism of U(IV) extraction with CYANEX 302 from nitrate medium was studied using a stirred Lewis cell and the authors reported that the extraction rate is controlled by a chemical reaction at the interface (12). The same cell was used by El- Dessouky et al. (13) to study the mechanism of Th(IV) extraction with CYANEX 272 also from nitrate medium and it was found that the extraction mechanism is governed by a chemical reaction in the bulk of the aqueous phase rather than at the interface. El-Hefny and Daoud (14) studied the extraction and separation of Th(IV) and Pr(III) from nitrate medium by CYANEX 301 and CYANEX 302 and reported that both reagents are prospective extractants for the Th(IV)/Pr(III) separation with higher values for CYANEX 302. The extraction and separation of Co(II) and U(VI) from different aqueous media by CYANEX 272 in kerosene was found to take the sequence nitrate > sulphate > chloride (15). CYANEX 921 was used for the extraction of U(VI), Nd(III) and Cr(III) from thiocyanate medium and the authors reported that this extractant could effectively extract the investigated metal ions and the separation of Nd(III) from Cr(III) and U(VI) in the investigated system is governed by the thiocyanate concentration (16). El-Nadi et al. (17) studied the extraction of La(III) and Sm(III) from nitrate medium by 1 Author jadaoud@yahoo.com 187

2 CYANEX 921, CYANEX 923 and CYANEX 925 in kerosene and found that the sequence of extraction of both metals takes the sequence CYANEX 921> CYANEX 923 >> CYANEX 925 with higher extraction of Sm(III) compared to La(III). These phosphine oxide extractants were also used to extract and separate Zr(IV) and Hf(IV) from nitrate medium and efficient Zr(IV)/Hf(IV) separation was obtained with CYANEX 925 (18). The extraction and separation of Zr(IV) and Nb(V) from nitrate medium with CYANEX 921 and TBP were studied and compared (19). Zaki et al. (20) studied the extraction of Be(II) and Al(II) from aqueous sulphate medium using CYANEX 921 and developed a process for the recovery of pure beryllium from Egyptian Beryl. El-Hefny et al. (21) prepared and used a sodium salt of CYANEX 272 to study the equilibrium and kinetics of Sm(III) extraction from chloride medium. Recently (22), CYANEX 923 was found to have high extraction ability and separation towards Pr(III), Nd(III) and Sm(III) from nitrate medium with a decreasing separation factor in the order S Sm/Pr > S Sm/Nd > S Nd/Pr. On the other hand, CYANEX reagents were successfully used to extract hazardous metals from different aqueous media. In this respect, Daoud et al. (23) studied the permeation of Cd(II) ions from aqueous phosphate medium through a supported liquid membrane (SLM) impregnated with CYANEX 302 in kerosene as carrier and assessed the conditions for removal of heavy metals from phosphate wastewater streams. The same authors (24) studied the extraction of Cd(II), Cu(II), Pb(II), Zn(II), Fe(III) and U(VI) from phosphoric acid and reported that Cd(II) could be selectively removed from phosphoric acid with the same SLM system containing CYANEX 302. Comparison of three liquid membrane technologies for the removal of Cd(II) from wet process phosphoric acid when using CYANEX 302 as extractant revealed that the rate of Cd removal and the values of transfer flux decreased in the order: non-dispersive solvent extraction (NDSX) > emulsion liquid membranes (ELM) > supported liquid membranes (SLM) (25). El-Hefny et al. (26) used CYANEX 921 in kerosene to extract and separate Co(II) and Ni(II) from thiocyanate medium. CYANEX 272 was used for Cr(III)/Cr(VI)separation from different nitrate, sulphate and chloride media and it was found that the extraction process is ph dependent and a process for recovery of highly pure Cr(III) is proposed (27). Continuous counter-current extraction and recovery of Zn(II) from simulated and real industrial waste resulting from rayon industry was carried out with CYANEX 272 using a horizontal mixer-settler and high efficiencies were obtained (28). El-Nadi et al. (29) used CYANEX 301 for the extraction and efficient separation of Zn(II) from Mn(II) from the leach solution of the black paste of spent MnO 2-Zn dry cell batteries. El-Hefny and Daoud (30) used CYANEX 302 to extract copper from different aqueous media. The extraction and separation of Zn(II), Fe(II), Fe(III) and Cd(II) with TBP and CYANEX 921 from chloride medium was studied by El-Dessouky et al. (31) who found that TBP is more suitable for the recovery of Zn(II) from pickling solution resulting from hot dipping galvanizing bath. Gasser et al. (32) studied the extraction of Co(II) from aqueous thiocyanate medium using emulsion liquid membrane (ELM) with CYANEX 923 in cyclohexane as extractant. CYANEX 923 and CYANEX 272 were used to recover and separate Cd(II), Co(II) and Ni(II) from chloride medium (33). Aly et al. (34) used an emulsion liquid membrane containing CYANEX 302 as carrier for the extraction of Cd(II), Cu(II) and Zn(II) from aqueous phosphate medium and reported that the used technique is fast and efficient for the removal of Cd(II) and Cu(II) from aqueous phosphate waste solution but not for Zn(II). El-Nadi et al. (35) used CYANEX 923 in kerosene to study the extraction of Zn(II), Fe(II) and Fe(III) from hydrochloric acid medium. El-Hefny et al. (36) used CYANEX 921, CYANEX 923 and CYANEX 925 in kerosene for the separation and recovery of Zn(II) and Co(II) from mixed sulphate/ thiocyanate solutions and reported that the selectivity between Zn(II) and Co(II) follows the order CYANEX 925 >CYANEX 923 > CYANEX 921. CYANEX 272 was also used in the recovery of Co(II) and Ni(II) from spent Nickel-Metal hydride batteries (37). The extraction and separation of Co(II) and Ni(II) from chloride medium was carried out using CYANEX 301 in kerosene (38). Negm et al. (39) used supported liquid membrane technique using CYANEX 301 in kerosene as carrier to remove heavy metals from water effluents. Gasser et al. (40) studied the transfer and separation of Zn(II) and Co(II) through a supported liquid membrane impregnated with CYANEX 925 in kerosene as carrier. Further, CYANEX reagents were also used for the extraction of platinum group metals. In this context, Ahmed et al. (41) studied the extraction of Pd(II) from nitrate solution by CYANEX 471X in 188

3 kerosene and reported that it is possible to selectively extract Pd from some interfering ions which may be found in spent nuclear fuel. In this context, the present work presents a brief survey on the work carried out in our laboratories on the extraction of valuable and hazardous elements from different aqueous media by CYANEX reagents. The potential use of these extractants for treatment of industrial waste for recovery and reuse of metals and pollution control is discussed. Application of CYANEX extractants on the extraction of some elements from waste solutions or from their ores is also presented. 2. EXPERIMENTAL 2.1. Chemicals and Reagents The CYANEX extractants listed in Table 1 and used in the different experiments were kindly offered by Cytec (USA) and used as received. CYANEX 272 which is the commercial name of bis (2,4,4-trimethylpentyl) phosphinic acid is a colourless to light amber liquid. CYANEX 301 or bis (2,4,4-trimethylpentyl) dithiophosphinic acid is a green liquid. CYANEX 302 which is the trade name of bis (2,4,4-trimethylpentyl) monothiophosphinic acid is a light amber liquid; CYANEX 272, CYANEX 301 and CYANEX 302 are present as dimers in aliphatic diluents (42,43) CYANEX 921 is an off-white waxy solid which contains 93% of trioctylphosphine oxide as the active substance (44) and is considered to be more advantageous than pure TOPO due to its relatively higher solubility in common hydrocarbon diluents (45). CYANEX 923 is a colorless liquid which comprises a mixture of four trialkylphosphine oxides, with the general formula R 3PO (14%), R 2R PO (42%), RR 2 PO( 31%) and R 3 PO(31%) and R 3 OPO (8%), in which R denotes n-octyl and R stands for n-hexyl group (46). CYANEX 925 or bis(2,4,4-trimethylpentyl) octylphosphine oxide is a colorless to light amber liquid claimed as a mixture of trialkylphosphine oxides containing normal and branched octyl groups (47). Alguacil et al. (48) state that this reagent is a mixture of only two compounds with the formula R 3PO and R 2R PO, where R= CH 3C(CH 3) 2CH 2CH(CH 3)CH 2(2,4,4-trimethylpentyl) and R =CH 3(CH 2) 7 (n-octyl). Kerosene (non-aromatic) was supplied by Misr Petrol Ltd., Egypt. Other diluents were of analytical reagent (AR) grade. The chemicals used in the preparation of the different aqueous media presented in this manuscript were also of AR grade and used without further purification. Table (1): The used CYANEX reagents CYANEX Extractants Chemical Formula Molecular weight Appearance CYANEX 272 Bis(2,4,4-trimethylpentyl) phosphinic acid (C 8H 17) 2P(O)OH M.W. 290 Colorless to light amber liquid CYANEX 301 Bis(2,4,4-trimethylpentyl) dithiophosphinic acid (C 8H 17) 2P(S)SH M.W. 322 Green liquid CYANEX 302 Bis(2,4,4-trimethylpentyl) monothiophosphinic acid (C 8H 17) 2P(S)OH M.W. 306 Light amber liquid CYANEX 923 Mixture of 4 trialkyl phosphine oxides R 3P=O Avg. M.W. 348 Colorless liquid CYANEX 925 Bis(2,4,4- trimethylpentyl)octylphosphine oxide (C 8H 17) 2P=O M.W. 386 Colorless to light amber liquid CYANEX 921 Trioctylphosphine oxide (TOPO) (C 8H 17) 2P=O M.W. 386 Off-white waxy solid CYANEX 471X Triisobutylphosphine sulphide (C 4H 9) 3P=S M.W. 234 Off-white crystalline solid 189

4 2.2. General In the batch experiments and before the extraction, a pre-equilibration step has been performed between the organic and aqueous phases alone without any metal in order to minimize the proton extraction (if any) during the extraction process. The metal was added in the pre-equilibrated aqueous phase which was then added to the equilibrated organic phase and shaken in stoppered glass tubes using a thermostated water bath shaker for enough time to reach equilibrium; the phases were then separated and the concentration of the metal ions in the aqueous phase in most cases were determined spectrophotometrically using a Shimadzu 160A double beam spectrophotometer. The metals concentration in the organic phases was determined by the difference in their concentration in the aqueous phase before and after extraction. The distribution ratio (D) was calculated from the ratio of the metals concentration in the organic to that in the aqueous phases. In cases where many metal ions were found in a mixture, their concentrations were determined with an atomic absorption spectrophotometer, Model S Series, Thermo-electron Corporation. In general, the extraction and stripping experiments were carried out with equal aqueous and organic volumes at o C, unless otherwise mentioned Techniques The extraction systems presented in this manuscript were carried out using conventional solvent extraction technique as well as other techniques. A stirred Lewis cell modified by Daoud et al. (49) was used for the kinetic studies carried out to learn about the mechanism of metals extraction in many systems. In supported liquid membrane investigations (SLM) used to study the transfer and concentration of heavy metals, the used horizontal cell and general procedures are described by Daoud et al. in a previous publication (23) ; another vertical cell was also used and described by Negm et al. (39). The preparation of the emulsion liquid membrane used in the extraction of Co(II) from thiocyanate medium is described by Gasser et al (32). In the application studies, continuous counter-current extraction was performed using a horizontal mixer-settler unit of the type MSU-0.5, which is a product of MEAB, Sweden. This unit contains sixteen mixer-settler stages and has the advantage that each unit can be hydrodynamically independent, which enables flexibility in selecting the number of stages and evaluation of the solvent extraction data (50). 3. RESULTS AND DISCUSSION 3.1-EXTRACTION OF VALUABLE ELEMENTS BY CYANEX REAGENTS A-Extraction of Elements of Nuclear Importance: Different types of CYANEX reagents have been successfully used for the extraction of uranium, thorium, zirconium, hafnium, niobium and beryllium from different media. 1-Extraction of U(VI), U(IV) and Th(IV) from nitric acid by CYANEX 272, CYANEX 301 and CYANEX 302 in kerosene (9) : Parallel studies on the extraction of U(VI), U(IV) and Th(IV) from nitric acid solution by CYANEX 272 in kerosene were carried out under similar experimental conditions. The results indicate that the extraction of the investigated ions increases with the increase in [CYANEX 272] and the decrease in the metal ions concentration; the increase in [H + ] and [NO 3- ] in the respective concentration ranges 1-5 and 3-5M increased the extraction percent of U(VI), U(IV) and Th(IV). The increase in the concentration of nitric acid in the range 0.1-5M decreased the extraction of U(VI) and Th(IV) while it increased the extraction of U(IV). The increase in temperature in the range 5-45 o C had a slight increasing effect while it had an inhibiting effect on the extraction of U(VI) and U(IV). 190

5 The extraction investigations of U(VI), U(IV) and Th(IV) by CYANEX 301 and CYANEX 302 indicate that they can also be used as efficient extractants for these ions from nitric acid medium. The investigated parameters have shown trends similar to that of the CYANEX 272 system. The investigated CYANEX extractants have the advantage of not extracting nitric acid and the efficiency of extraction at low extractant concentrations. The maximum extraction of U(VI) and U(IV) from nitric acid takes the sequence CYANEX 272 > CYANEX 302 > CYANEX 301. The extraction of Th(IV) takes the sequence CYANEX 301~ CYANEX 302 > CYANEX Equilibrium and Mechanism of U(IV) extraction from nitric acid medium with CYANEX 302 in kerosene (12) Investigations on the extraction equilibrium of U(IV) from nitric acid medium using CYANEX 302 in kerosene were carried out under equilibrium conditions. Taking into consideration the great tendency of water molecules in the acid solution to coordinate directly around U(IV) and the dimeric form of CYANEX 302 in aliphatic diluents, the extraction equilibrium is given by: U(H 2O) x 4+ + NO (HA) 2org. U(NO 3)A 3(HA) 3(H 2O) x-7 org. + H H 2O Kinetic investigations using a stirred Lewis cell have shown that the extraction rate of U(IV) by CYANEX 302 increases with increasing the nitric acid and extractant concentrations as well as the interfacial area. The results are interpreted by a reaction mechanism where the extraction process of U(IV) is controlled by a chemical reaction at the interface rather than in the bulk phase. 3- Extraction of U(VI) from Aqueous Nitrate Medium with CYANEX 301 in Kerosene (11) The extraction of U(VI) as well as Nd(III), Fe(II) and Co(II) with CYANEX 301 in kerosene from aqueous nitrate medium of constant ionic strength has been investigated. The results indicate that this extractant is efficient for the recovery of U(VI), Co(II) and Fe(II) while Nd(III) was not extracted under the investigated conditions. Stripping of the metals from the loaded organic solutions indicates that the stripping efficiency takes the sequence H 2SO 4 > HCl >HNO 3 ; H 2SO 4 is preferred for the sequential separation of U(VI), Co(II) and Fe(II) by monitoring its molarity in the stripping solution. The difference in the extraction and stripping behavior of the investigated metal ions was used to optimize the conditions for a sequential separation of U(VI) as well as Nd(III), Fe(II) and Co(II) from 0.1M nitrate solution. 4-Extraction of U(VI) from Aqueous Solution Using CYANEX 272 in Kerosene (15) The extraction and separation of U(VI) and Co(II) with CYANEX 272 in kerosene from different media was explored. The results indicate that the investigated extractant could extract U(VI) and Co(II) efficiently from aqueous media of ph 3 and 8, respectively. The increase in sulphate ion concentration decreased the extraction of U(VI) while it increased the extraction of Co(II); the increase in nitrate ion concentration had nearly no effect on U(VI) and decreased Co(II) concentration. The extraction equilibrium of U(VI) was reached after 5 min. while the extraction equilibrium of Co(II) was reached after 140 min. which enables their separation on kinetic basis. The increase in temperature decreased U(VI) extraction while it increased the extraction of Co(II). Sulphuric acid was found to be effective for stripping U(VI) while hydrochloric and sulphuric acids stripped Co(II) efficiently from their loaded organic solutions. However, the use of nitric acid as stripping agent is preferred for the separation between the two ions as it gives quantitative stripping of Co(II) and negligible stripping of U(VI) under the same experimental conditions. 191

6 The maximum U(VI)/Co(II) separation from different aqueous media was found to take the sequence: Nitrate > sulphate > chloride. 5- Extraction of U(VI) from Thiocyanate Medium with Cyanex 921 In Kerosene (16) CYANEX 921 in kerosene was used for the extraction of U(VI), Nd(III) and Cr(III) from thiocyanate medium and found to be effective for the extraction of the investigated metal ions. The predominant species of U(VI), Nd(III) and Cr(III) in the thiocyanate medium under the used experimental conditions were found to be [UO 2(SCN) 3] -, Nd(OH) 3 and [Cr(SCN) 2] +. Sequential separation of these ions could be reached by varying the extraction and stripping conditions. The separation of Nd(III) from Cr(III) and U(VI) with CYANEX 921 in kerosene could be governed by varying the thiocyanate concentration in the aqueous medium. As the thiocyanate concentration decreases, the separation of Nd/Cr and Nd/U increases. 6- Equilibrium and Mechanism of Th(IV) Extraction by CYANEX 272 in Kerosene from Nitrate Medium (13) The extraction behavior of Th(IV) from aqueous nitrate medium by CYANEX 272 in kerosene has been studied under equilibrium conditions to elucidate the stoichiometry of the extracted species which was found to be Th(OH) 3A.(HA) 3, where HA denotes CYANEX 272. Kinetic investigations on the same system using the modified Lewis cell (49) used before have indicated that the reaction is first- order dependent on CYANEX 272 concentration, inverse firstorder dependent on thorium and hydrogen ion concentration and independent of [NO 3- ]. The proposed mechanism for the extraction process assumes that the controlling reaction takes place in the aqueous phase rather than at the interface. 7- Extraction of Th(IV) from Nitrate Medium with CYANEX 301 and CYANEX 302 in Kerosene (14) The extraction properties of CYANEX 301 and CYANEX 302 in kerosene towards Th(IV) and Pr(III) in aqueous nitrate medium has been investigated. The extraction process of Th(IV) and Pr(III) by both extractants is endothermic. The separation of both metal ions by CYANEX 301 and CYANEX 302 could be controlled by varying the extractant and nitrate concentrations as well as the ph of the aqueous medium. The results indicate that CYANEX 301 and CYANEX 302 are prospective extractants for Th(IV)/Pr(III) separation from aqueous nitrate medium. CYANEX 302 is more effective for separating Th(IV) from Pr(III). The maximum calculated separation factors S Th/Pr by CYANEX 302 and CYANEX 301 at [H + ]=0.032M are 5.74x10 11 and 2.99x10 8, respectively. 8- Extraction of Zr(IV) from Nitric Acid Solutions Using CYANEX 272, CYANEX 301 and CYANEX 302 in Kerosene (10) Extraction investigations on the extraction of Zr(IV) from 3M nitric acid by CYANEX 272, CYANEX 301 and CYANEX 302 in kerosene have indicated that these extractants are efficient for Zr(IV) extraction; the maximum extraction increases in the sequence CYANEX 301 < CYANEX 302 < CYANEX 272. The increase in temperature in the range o C increased the extraction process. The increase in temperature from 15 to 35 O C in case of CYANEX 272 leads to nearly complete extraction of 192

7 Zr(IV) from 3M nitric acid (>99.99%) and remains constant with further increase in temperature; in case of CYANEX 302 this maximum extraction was reached at 55 o C. On the other hand, the increase in temperature has a relatively small effect on the extraction of Zr(IV) with CYANEX 301, where a maximum extraction of 64% was reached at 55 o C. Complete stripping of Zr(IV) (>99.9%) from the loaded CYANEX 272 and CYANEX 302 was reached with 2 and 2.5M H 2SO 4, respectively; quantitative stripping of the metal (76%) from loaded CYANEX 301 solution was obtained with 2.5M H 2SO 4. The investigated extractants are promising reagents for the removal of Zr(IV) from radioactive waste solutions. 9- Extraction and Separation of Zr(IV) and Hf(IV) from Nitric Acid Medium with CYANEX 921, CYANEX 923 and CYANEX 925 in Kerosene (18) Zirconium and hafnium co-exist in nature but have opposite nuclear characteristics and have very similar chemical properties; they have to be separated prior to their transformation into pure metals. Zirconium metal should contain less than 100 ppm hafnium for use in nuclear reactors. Zirconium is used in nuclear reactors as structural and container material and hafnium is used as a control material in water-cooled nuclear reactors and rectifiers. The extraction of Zr(IV) and Hf(IV) by CYANEX 921, CYANEX 923 and CYANEX 925 is relatively fast and endothermic. In slightly acidic solution zirconium and hafnium are mainly present as the oxycations MO 2+, and in slightly nitrate medium MO(NO 3) 2 is the main metal species (51). Assuming that neutral organophosphorus extractants extract neutral metal ions by solvation, the extraction process for the investigated systems can be represented as: MO 2+ (aq) + 2NO - 3(aq) + xl (org) MO(NO 3) 2. xl (org) Where, L stands for either of the three extractants (CYANEX 921, CYANEX 923 or CYANEX 925) and x represents the number of extractants involved in the extracted Zr(IV) or Hf(IV) species. Based on the obtained results, the main extracted zirconium species were found to be ZrO(NO 3) 2.2CYANEX 921, ZrO(NO 3) 2.3CYANEX 923 and ZrO(NO 3) 2.2CYANEX 925 with respective average extraction constants , and In case of hafnium, the main extracted species are HfO(NO 3) 2.2CYANEX 921, HfO(NO 3) 2.3CYANEX 923 and HfO(NO 3) 2.CYANEX 925 with respective extraction constants , and Stripping investigations indicate that dilute nitric acid leads to good separation of Zr(IV) from Hf(IV). The selectivity between Zr(IV) and Hf(IV) with the three investigated CYANEX reagents follows the order: CYANEX 925 > CYANEX 923 > CYANEX 921 The separation factor with CYANEX 925 under the used experimental conditions reaches 40.7 which is higher than that obtained by TBP and reported to be 10 (52 ) and that obtained by CYANEX 272 which reaches 34 (53). Besides, the extraction of zirconium with CYANEX 925 reaches 92% which is higher than that reported in other works (53,54). 193

8 10- Extraction and Separation of Zr(IV) and Nb(V) from Nitric Acid Medium with CYANEX 921 (19) and CYANEX 925 (55) in Kerosene The potential use of CYANEX 921 and CYANEX 925 in kerosene for the extraction and separation of Zr (IV) and Nb(V) from nitric acid medium was explored and compared with TBP under similar experimental conditions. The results indicate that the CYANEX reagents are more reactive for the extraction of Zr(IV) and Nb(V) compared with TBP due to their higher basicity. The extraction constant of Zr(IV) in the investigated systems was found to be , and for CYANEX921, CYANEX 925 and TBP, respectively. Hydrochloric and nitric acids were found to be efficient for stripping Zr(IV) from loaded CYANEX 921; sulphuric acid stripped Zr(IV) efficiently from loaded CYANEX 925 while nitric acid stripped Zr(IV) from loaded TBP solutions. The values of the extraction constants of Nb(V) were found to be , and for CYANEX 925, CYANEX 921 and TBP systems, respectively. Hydrofluoric acid was found to be suitable for stripping Nb(V) from loaded CYANEX 921, CYANEX 925 and TBP in kerosene solutions. Based on the extraction results, the maximum separation factor of Zr(IV) from Nb(V) by the investigated extractants were found to be 2.30, 5.40 and 1.90 for CYANEX 921, CYANEX 925 and TBP, respectively. Separation based on the difference in the stripping behavior indicates that in CYANEX 921 system Zr(IV) could be first stripped with any mineral acid (hydrochloric, sulphuric or nitric) then Nb(V) is stripped with hydrofluoric acid, oxalic acid, sodium carbonate or potassium hydroxide. In CYANEX 925 system, Zr(IV) is also first stripped with any mineral acid then Nb(V) is stripped with sodium hydroxide. 11- Extraction of Beryllium and Aluminum from Aqueous Sulphate Solution with CYANEX 921 in Kerosene (20) Beryllium is used in nuclear reactors as a neutron reflector and moderator based on its high melting point, low neutron absorption and high scattering cross section. Aluminum has also a relatively low thermal neutron cross section, low cost and high corrosion resistance at low temperature which makes it suitable for use as a structural material in nuclear reactors; pure aluminum (>99.9%) has been extensively used as cladding material and containers for neutron irradiated materials. Beryl which is one of the most significant ores of beryllium is a beryllium aluminum silicate and contains <12% BeO, 17-19% Al 2O 3, 64-70% SiO 2, 1-2% alkali metal oxides, and minor amounts of other oxides. Due to the great similarity of the chemical properties of Be and Al, the separation between them is of special interest. Extraction investigations have indicated that Be(II) is highly extracted by CYANEX 921 from an aqueous 0.001M sulphate solution at ph 9.0, while Al(III) is highly extracted from a similar solution at ph 5.0. The increase in temperature was found to decrease the extraction of Be(II) while it increased the extraction of Al(III). CYANEX 921 (which contains about 93% trioctylphosphine oxide as active substance (56)) ) was found to give higher extraction percent of Be(II) and Al(III) compared with pure TOPO under similar extraction conditions, except for Al(III) in the ph range Based on the obtained results, separation of beryllium from aluminum and recovery of pure beryllium from beryl mineral were studied. A flow chart for the Be/Al separation process was developed and applied to recover pure Be(II) from Egyptian beryl. 194

9 B-Extraction of Lanthanides and Rare Earth Elements by CYANEX Reagents: 1-Extraction of La(III) and Sm from nitrate medium with CYANEX 921, CYANEX 923 and CYANEX 925 in kerosene (17) The extraction of La(III) and Sm(III) from nitrate medium by CYANEX 921, CYANEX 923 and CYANEX 925 in kerosene has been investigated. The stoichiometry of the extracted metal species were found to be M(NO 3) 3.3CYANEX921, M(NO 3) 3.2CYANEX 923 and M(NO 3) 3.CYANEX 925, where M stands for La or Sm. The results indicate that La(III) and Sm(III) are extracted by CYANEX 921, CYANEX 923 and CYANEX 925 in kerosene ; the extraction of both metals takes the sequence CYANEX 921> CYANEX 923 >> CYANEX 925 with higher extraction of Sm(III) compared to La(III) in the three investigated systems. The increase in temperature decreased the extraction extent of both metal ions. Striping investigations indicate that mineral acids efficiently strip La(III) and Sm(III) from their loaded organic phases but dilute nitric acid (0.75M ) is preferred as it can enhance La/Sm separation after two stripping stages at O:A phase ratio= 1 and 25 o C. 2- Equilibrium and Mechanism of Sm(III) Extraction from Chloride Medium Using Sodium Salt of CYANEX272 in Kerosene (21) In order to improve Sm(III) extraction by the acidic form of CYANEX 272, the extractant was converted to the sodium form by the addition of a stoichiometric amount of sodium hydroxide (57,58). The extent of neutralization was found to be limited to 60% due to the polymerization of the organic phase beyond 75% neutralization. This partial neutralization reaction is represented as: Na + (aq) + ½(HA) 2(org) NaA (org) + H + (aq) (1) Thus the acidic as well as the neutral form of the extractant take part in the extraction process of samarium which is considered to be Sm(OH) 2+ ; the sodium ion in the extractant is replaced by the samarium ion according to the reaction: Sm(OH) NaA.2HA (org) Sm(OH)A 2.2HA (org) + 2 Na + (2) Based on equations (1) & (2), the extraction of Sm under equilibrium conditions can be represented by the following equation: Sm(OH) (HA) 2(org) Sm(OH)A 2.2HA (org) +2H + (aq) (3) Equation (3) explains the results obtained from the slope analysis method. Therefore, K ex = D [H + ] 2 (aq.) / [(HA) 2] 2 (org) Kinetic investigations on the extraction of Sm(III) from chloride medium by the prepared sodium salt of CYANEX 272 using the modified Lewis cell were also carried out. The proposed mechanism of Sm(III) extraction in the investigated system indicates that the rate of extraction is controlled by a slow reaction in the bulk of the aqueous phase rather than at the interface. 195

10 3-Extraction of Pr(III) from Aqueous Nitrate Solution with CYANEX 301 and CYANEX 302 in Kerosene (14) The extraction of Pr(III) from nitrate medium by CYANEX 301 in kerosene under equilibrium conditions indicates that the extraction process increases with the increase in the extractant and nitrate concentration and the decrease in hydrogen ion and metal concentration. Based on the slope analysis method of the obtained results, the stoiciometry of the extracted metal species was elucidated and found to be Pr(NO3)A 2(HA) 3, where HA denotes CYANEX 301. The effects of the different parameters on the extraction of Pr(III) by CYANEX 302 in kerosene have shown trends similar to that of CYANEX 301 system with different slopes. The stoichiometry of the extracted Pr(III) species was found to be Pr(NO 3)A 2. The increase in temperature in the range 5-45 o C was found to have a slight enhancing effect on the extraction of Pr(III) by CYANEX 301 or CYANEX 302 in kerosene. 4- Extraction of Nd(III) from Thiocyanate Medium with CYANEX 921 in kerosene (16) Extraction investigations on the extraction of Nd(III) from thiocyanate medium with CYANEX 921 in kerosene have shown that the extraction increases with the increase in the extractant concentration while neither the increase in [H + ] ion nor that of [SCN - ] had an effect on the extraction process in the investigated ranges. The increase in Nd(III) concentration slightly increased its extraction with CYANEX 921 while the increase in temperature in the range o C slightly decreased the extraction process. The stoichiometry of the extracted Nd(III) species was found to be Nd(OH) 3.2 CYANEX Extraction of Pr(III), Nd(III) and Sm(III) from Nitric Acid Medium by CYANEX 923 in Kerosene (22) The extraction of Pr(III), Nd(III) and Sm(III) from nitric acid medium by CYANEX 923 in kerosene at 25 o C under equilibrium conditions has been carried out. Based on the slope analysis method of the obtained experimental data the stoichiometry of the extracted species were found to be Pr(NO 3) 2(OH).2CYANEX923, Nd(NO 3) 2(OH).2CYANEX923 and Sm(NO 3) 2(OH). 2CYANEX 923. The proposed complexes were verified by IR spectroscopic investigations of the organic phase before and after extraction of each of the investigated lanthanides. The increase in temperature through the range o C decreased the extraction efficiency of Pr(III), Nd(III) and Sm(III) by CYANEX 923 in kerosene under the used experimental conditions. Stripping investigations of the studied lanthanides from their loaded organic phase indicate that a maximum stripping of 82 and 72% of Pr(III) was achieved with 1M H 2SO 4 and 1M Na 2CO 3, respectively; a maximum stripping of 83% Nd(III) was achieved with 0.5M H 2SO 4 and 1M HCl; in case of Sm(III), 66.80% stripping was obtained with 1M H 2SO 4 and 4M Na 2CO 3. The separation feasibility between the investigated lanthanides have shown that the separation factor decreases in the order S Sm/Pr > S Sm/Nd > S Nd/Pr+. 6-Extraction of Ce(IV), Y(III) and Yb(III) from Nitric Acid Medium with CYANEX 923 in Kerosene (59) The potential use of CYANEX 923 in kerosene for the extraction of Ce(IV), Y(III) and Yb(III) from nitric acid medium by CYANEX 923 in kerosene was also investigated under the same experimental conditions of the previous study on Pr(III), Nd(III) and Sm(III) by the same extractant. The results indicate that CYANEX 923 in kerosene is also an efficient extractant for Ce(IV), Y(III) and Yb(III) extraction from nitric acid solution. The extracted metal species were found to be Ce(NO 3) 3(OH).2 CYANEX 923, Y(NO 3) 2(OH).2 CYANEX 923.H 2O and Yb(NO 3) 2(OH).2 CYANEX 923.H 2O. The proposed complexes were also 196

11 verified by IR spectroscopic investigations of the organic phase before and after extraction of each of the investigated rare earth elements. The stripping of Ce(IV) from its loaded organic solution was found to reach a maximum of 89.7 and 77.5% with 1M HCl and 1M Na 2CO 3, respectively; a maximum stripping of Y(III) of 68.5 and 72% was achieved with 1M HCl and 0.5M H 2SO 4, respectively; the stripping of Yb(III) reached a maximum of 46 and 52% with 0.5M H 2SO 4 and 1M HCl, respectively. The separation between Ce(IV), Pr(III), Nd(III), Sm(III) Y(III) and Yb(III) from nitric acid medium by CYANEX 923 in kerosene under similar experimental conditions indicates that the extraction with this extractant favors the separation of Sm(III) from the other lanthanides in the order S Sm/Ce > S Sm/Y > S Sm/Pr > S Sm/Nd. The relation between the extraction constant (K ex) and the atomic number of the investigated rare earth elements indicates that it is possible to separate Y(III) from the light lanthanides {Ce(IV), Pr(III), Nd(III)}, the medium {Sm(III)} and the heavy one {Yb(III)}. This implies the high ability of CYANEX 923 in the investigated system for the extraction and separation of rare earth elements from nitrate medium. The difference in the stripping behavior of the investigated rare earths indicate that Na 2CO 3 could strip the light lanthanides {Ce(IV), Pr(III),Nd(III) and Sm(III)} in the aqueous phase leaving the heavy rare earths (Y(III) and Yb(III) in the organic phase. Monitoring the extraction temperature could also lead to good separation between the investigated rare earths. Application of the obtained results on a sample of Egyptian monazite indicates that the used system could be efficiently used for extraction and separation of Ce(IV), Pr(III), Nd(III), Sm(III) Y(III) and Yb(III) from the monazite after its alkaline dissolution and the removal of thorium and dilution from the solution. C- Extraction of Platinum Group Metals by CYANEX Reagents: Extraction of Palladium from Nitric Acid Medium by CYANEX 471X (41) Palladium is found as a fission product in spent nuclear fuel; the increasing demands of Pd faced with a limited and decreasing source of this metal makes spent nuclear fuel a potential source of palladium and an alternative to its mineral contributors. After cooling and decladding, the spent nuclear fuel is dissolved in nitric acid, which makes the extraction of palladium from nitrate medium a matter of great importance. Extraction of Pd(II) from nitric acid solution was carried out by CYANEX 471X in kerosene using n-octanol as a modifier. The stripping of Pd from the loaded organic phase was performed with stabilized thiosulfate solution. The results indicate the possibility of separating Pd from some interfering which may be found with palladium in the spent nuclear fuel as Co(II), Fe(II), Cu(II), Cd(II) and Zn(II) as the extraction of Pd(II) reached 72% while the extraction of these ions was less than 5%. The extraction of palladium by CYANEX 471X was also carried out from other acidic media, namely, hydrochloric and sulphuric acid. The results indicate that the extraction of Pd from the investigated aqueous media decreases in the order sulphuric > nitric > hydrochloric acid. A method is developed for the recovery of Pd, Pt and Rh from a synthetic chloride solution similar to that expected from the leaching of spent automotive catalyst and the recovery of Pt and Pd was found to be 70 and 75%, respectively. Higher percent recovery could be obtained with higher org.: aq. ratio or with repeated extraction (continuous extraction). 197

12 Hydrochloric acid is more preferred for the recovery of Pd and collector metal ions from automotive catalysts due to the ease of recovery of platinum as diammoniumchloroplatinate (NH 4) 2PtCl Extraction of Hazardous Elements by Cyanex Reagents The fate of toxic pollutants in the environment represents a main risk to human health. Heavy metals are among the toxic pollutants which are not biodegradable and are characterized by a long environmental persistence which constitutes a significant pollution problem. Wastes produced from nuclear and industrial activities contain important amounts of heavy metals which recovery is necessary due to their hazardous effect and inherent value. CYANEX reagents have been widely used to remove the heavy metals from different aqueous media using different techniques. 1-Removal of Cd(II) from Phosphate Medium by CYANEX 302 in Kerosene (23,24,25) The extraction of Cd(II), Cu(II) and Zn(II) from aqueous phosphate medium with CYANEX 302 in kerosene has been carried out under equilibrium conditions. The permeation of Cd(II) ions through a supported liquid membrane (SLM) consisting of a flat disc cellulose nitrate membrane immobilizing a CYANEX 302 in kerosene as carrier in a two-compartments cell has been investigated. The results indicate that the investigated SLM system could be used for complete removal of 4.45x10-4 Cd from an aqueous phosphate medium of ph 2. In addition, the used system is selective for Cd-Cu separation (23). The individual extraction and stripping of Cd(II), Cu(II), Zn(II), Pb(II) and U(VI) from 5M phosphoric acid by CYANEX 302 in kerosene was also studied under equilibrium conditions. The results indicate the complete extraction of Cd(II) with a partial extraction of Cu(II) while Zn(II), Pb(II) and U(VI) were nearly not extracted under the used experimental conditions. The permeation of these ions through a SLM consisting of a flat sheet cellulose nitrate immobilizing CYANEX 302 in the same cell has also been investigated; the individual transfer of the investigated ions through this cell showed its efficiency for the extraction and stripping of Cd and Cu but not for the other ions with a much lower rate for Cu. The investigated SLM process could be used for the selective of removal of Cd from wet process phosphoric acid (24). The comparison of three liquid membrane technologies, namely, emulsion liquid membrane (ELM), SLM and non-dispersive solvent extraction (NDSX) for the removal of Cd from wet process phosphoric acid when using CYANEX 302 as carrier has been investigated. A methodology has been developed for the comparison of the three membrane technologies based on solvent extraction and their removal of Cd from phosphoric acid. The results and methods employed could be extended to different applications (25). 2- Extraction and Separation of Co(II)and Ni(II) from Thiocyanate Medium Using CYANEX 921 in Kerosene (26) The extraction of Co(II) and Ni(II) from thiocyanate medium with CYANEX 921 in kerosene was carried out under equilibrium conditions. The results indicate that CYANEX is efficient for extraction of both metals. The predominant species of Co(II) and Ni(II) in NaSCN medium under the used experimental conditions were proposed to be [Co(SCN) 4] 2- and [Ni(SCN) 3] -. The separation between Co and Ni was found to be possible with dilute sulphuric acid which is able to strip nickel after 4 stripping stages leaving cobalt in the organic phase. 3- Extraction and Separation of Cr(III)/Cr(VI) from Different Aqueous Media Using CYANEX 272 in Kerosene (27) The extraction of Cr(III) and Cr(VI) from aqueous chloride, sulphate and nitrate media with CYANEX 272 in kerosene was carried out under equilibrium conditions. The results indicate that 198

13 CYANEX 272 is more selective for Cr(III) than Cr(VI) with relatively higher separation from chloride medium. The separation between Cr(III) and Cr(VI) was found to increase with the increase in the nitrate and chloride concentrations in the aqueous medium while the increase in sulphate concentration decreased the separation between both anions. The stripping of Cr(III) from loaded organic solution is quantitative with 6M sulphuric acid. The recovered Cr(III) from the strip liquor is highly pure (99%) and could be used for industrial purposes. The effect of interfering ions, namely, Fe(III) and Al(III) which are found in addition to Cr(III) with high concentration of chloride in tanning bath waste solution was investigated. The results indicate that these interfering ions could be neglected when carrying out the extraction of Cr(III) from solutions of ph 5, which was found to be optimum. 4 -Extraction and Recovery of Zn(II) from Aqueous Waste Solution with CYANEX 272 Using a Horizontal Mixer-Settler Unit (28) The extraction of Zn(II) with CYANEX 272 in kerosene from aqueous sulphate, chloride and nitrate has been investigated under equilibrium conditions. The effect of the different anions on the extraction of Zn from the aqueous medium was found to be in the sequence: sulphate > nitrate > chloride Stripping investigations with mineral acids indicate that the stripping percent of Zn(II) from the loaded organic phase takes the order HNO 3 > HCl > H 2SO 4. However, stripping with sulphuric is more preferred due to the ease of electrowinning of zinc from non-oxidizing acids. Extraction of Zn(II) from industrial waste solution resulting from rayon industry and also from a simulated solution by counter-current extraction using a horizontal mixer-settler unit was carried out based on the bench scale results. The results show that the extraction efficiency of Zn(II) with CYANEX 272 from simulated and real waste solution is 97 and 94%, respectively, whereas the stripping efficiency is ~ 96 % for both processes. 5- Recovery of Zn(II) from the Black Paste of Spent MnO 2-Zn Dry Cell Batteries with CYANEX 301 in Kerosene (29) Leaching Zn and Mn from the black paste of spent batteries with sulphuric or hydrochloric acid solutions showed that sulphuric acid is more efficient for leaching. Extraction of Zn and Mn from the leaching sulphate solution was carried out with CYANEX 301 in kerosene. The increase in the acid concentration slightly increased the extraction of Mn while it decreased the extraction of Zn; the extraction of Zn is higher than Mn. Selective stripping of Zn from the loaded organic phase was successfully performed with 5M HCl solution. Application of the studied method on the leaching sulphate solution of the spent MnO 2-Zn dry cell batteries shows the efficiency of the process, where the extraction and stripping of Zn(II) are 98% and 99%, respectively. 6- Extraction of Cu(II) from Different Aqueous Media with CYANEX 302 in Kerosene (30) The extraction of copper from sulphate, chloride and nitrate solutions was carried out with CYANEX 302 in kerosene. The results indicate that CYANEX 302 is a potential extractant for copper from aqueous sulphate, chloride and nitrate waste solutions. The proposed extraction equilibrium assumes that copper is first extracted as Cu 2+ then in the formed CuA 2 (HA) 2 complex copper is reduced to Cu + while CYANEX 302 is correspondingly oxidized to disulphide; this proposal was supported by the spectrophotometric measurements which indicated the absence of the characteristic peak of Cu(II) in the organic phase in spite of the decrease 199

14 in the Cu(II) concentration in the aqueous phase after extraction. Stripping of Cu(I) from the loaded organic solution was successfully performed with 4M nitric acid which acts as oxidizing agent and reoxidizes the monovalent copper in the organic phase to its divalent state. 7-Extraction and Separation of Zn(II), Fe(II), Fe(III) and Cd(II) from Chloride Medium with CYANEX 921 in Kerosene (31) The extraction of Zn(II), Fe(II), Fe(III) and Cd(II) from chloride medium with CYANEX 921 in kerosene was carried out under equilibrium conditions. Based on the slope analysis of the obtained results, the stoichiometry of the extracted species was found to be HZnCl 3.2CYANEX921, HFeCl 4.CYANEX 921 and H 2CdCl 4.3CYANEX 921. Comparison of the results of extraction obtained with CYANEX 921 and those obtained with TBP under similar conditions indicates that TBP is a better extractant for the investigated metal ions from chloride medium. 8- Extraction of Co(II) from Thiocyanate Medium with CYANEX 923 in Cyclohexane (32) The extraction equilibrium of Co(II) from thiocyanate medium by CYANEX 923 in cyclohexane was carried out under equilibrium conditions and the stoichiometry of the extracted metal species was found to be Co(SCN) 2.2CYANEX 923. Sulphuric acid was found to be efficient for stripping Co(II) from the loaded organic phase. The extraction of Co(II) from aqueous thiocyanate medium into emulsion liquid membrane (ELM) using CYANEX 923 as carrier was also studied. The effects of the different parameters as stirring speed, surfactant concentration, carrier concentration, internal phase stripping acid conc.etc..on the emulsion stability were investigated. The applicability of the prepared membrane containing CYANEX 923 as extractant and SPAN 80 as surfactant for the removal and concentration of Co(II) from thiocyanate solution indicates that it is possible to recover 95% of cobalt in the inner phase after 10 min. of contact time with a concentration factor of 5. 9-Recovery of Cd(II), Co(II) and Ni(II) from Chloride Medium with CYANEX 923 and CYANEX 272 in Kerosene (33) The extraction of Cd(II), Co(II) and Ni(II) from chloride medium by CYANEX 923 and CYANEX 272 in kerosene was investigated. The results indicate that CYANEX 923 could extract Cd(II) from 1M HCl solution, while Co(II) and Ni(II) are not nearly extracted. The increase in HCl, H +, Cl - and CYANEX 923 concentration increased the extraction of Cd(II), while the increase in temperature decreased the extraction process. Dilute HCl solution is effective for the quantitative stripping of Cd. Co(II) was found to be extracted with CYANEX 272 in kerosene leaving Ni(II) in the aqueous solution. Sulphuric acid could efficiently strip Co(II) from its loaded organic solution. The difference in the extraction and stripping behavior of Cd(II), Co(II) and Ni(II) from chloride medium could be used for their sequential separation from their mixture. 10- Extraction of Cd(II), Cu(II) and Zn(II) from Aqueous Phosphate Medium Using an Emulsion Liquid Membrane Containing CYANEX 302 as Carrier (34) The extraction of Cd(II), Cu(II) and Zn(II) from aqueous phosphate medium using an emulsion liquid membrane (ELM ) containing CYANEX 302 as carrier has been investigated. The results indicate that the prepared ELM is a fast and efficient technique for the removal of Cd(II) and Cu(II) from aqueous phosphate medium but not for Zn(II). 200

15 11-Extraction of Zn(II), Fe(II) and Fe(III) from Hydrochloric Acid Medium by CYANEX 923 in Kerosene (35) The results of the extraction of zinc and iron from hydrochloric acid medium with CYANEX 923 in kerosene indicates that CYANEX 923 could be considered as an efficient extractant for Zn(II) and Fe(III) extraction but not Fe(II). Slope analysis of the results of the effects of the different parameters indicates that the stoichiometry of the extracted species is ZnCl 2.3CYANEX 923 and FeCl 3.3CYANEX 923. Average stripping of Zn(II) and Fe(III) from the loaded organic solutions was attained with dilute mineral acids in one stripping stage, which indicates that three stages of stripping are needed to improve the stripping percent. 12-Extraction of Zn(II) and Co(II) from a Mixed Sulphate/Thiocyanate Solution with CYANEX 921, CYANEX 923 and CYANEX 925 in Kerosene (36) The extraction of Zn(II) and Co(II) from a mixed sulphate and thiocyanate solutions with CYANEX 921, CYANEX 923 and CYANEX 925 in kerosene has been investigated. The results indicate that the extraction of these metal ions by the investigated extractants takes the sequence: CYANEX 923 > CYANEX 921 > CYANEX 925, and Zn(II) was always more extracted than Co(II) in the investigated systems. The separation between Zn(II) and Co(II) by the investigated extractants could be controlled by varying the H + concentration of the aqueous medium. The selectivity between Zn and Co follows the order CYANEX 925 > CYANEX 923 > CYANEX 921. The extraction process with CYANEX 925 was applied for the separation of Zn from spent Ni- MH batteries leached by sulphuric acid and found to be successful. 13-Recovery and Separation of Co(II) and Ni(II) from Spent Nickel-Metal Hydride Batteries with CYANEX 272 in Kerosene (37) The extraction and separation of Co(II) and Ni(II) from the leach sulphate solution of spent Ni- MH spent batteries with CYANEX 272 in kerosene was carried out. The results indicate that CYANEX 272 extracts Co(II) efficiently while it hardly extracts Ni(II) under similar conditions. The separation feasibility between Co(II) and Ni(II) with CYANEX 272 is greatly affected by the ph of the solution; a separation factor of 1650 was obtained at ph 6 which is much higher than that obtained when using HDEHP as extractant under similar experimental conditions. 14-Extraction and separation of Co(II) and Ni(II) from Chloride Medium with CYANEX 301 in Kerosene (38) The results of the extraction investigations of Co(II) and Ni(II) from chloride medium by CYANEX 301 in kerosene indicate that both metals are extracted by this reagent. The equilibrium of Co(II) extraction was reached after 1 min. while that of Ni(II) after 180 min. The increase in temperature slightly decreased the extraction of Co(II) while it increased the extraction of Ni(II). Co(II) could be stripped selectively from the loaded organic solutions with mineral acids in the sequence: H 2SO 4> HCl > HNO 3. Co(II) could be separated from Ni(II) from their admixture after few minutes of extraction with 15% CYANEX 301 in kerosene at 25 o C. 15-Removal of Co(II), Ni(II), Zn(II) and Cd(II) from Water Effluents Using SLM Impregnated with CYANEX 301 in Kerosene (39) 201