Potassium permanganate as an oxidant in the remediation of soils polluted by Bonny light crude oil

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1 Sky Journal of Soil Science and Environmental Management Vol. 3(2), pp. 4-19, February, 2014 Available online ISSN Sky Journals Full Length Research Paper Potassium permanganate as an oxidant in the remediation of soils polluted by Bonny light crude oil Achugasim O *., Ojinnaka C. M and Osuji L. C. Department of Pure and Industrial Chemistry, University of Port Harcourt, Rivers State, Nigeria. Accepted 30 December, 2013 Ability of potassium permanganate as a chemical oxidant in the removal of hydrocarbons from crude oil polluted soils was evaluated in this research. Gas chromatography (GC) was used to monitor the depletion of three broad hydrocarbon groups: polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbon (TPH) and benzene, toluene, ethylbenzene, xylene(btex). Sandy soil samples polluted with bonny light crude oil were treated with potassium permanganate at the acidic, neutral and basic ph media. Hydrocarbon removal controlled by an unpolluted sample of soil crude oil mixture was found to be ph dependent with most of the depletions occurring at acidic phs. The removal of aromatic hydrocarbons (PAH and BTEX) was efficient even though the oxidant did not effect good removal of aliphatic hydrocarbons (TPH). This could be attributed to the mode of reaction of permanganates which involves electrons unlike other oxidants like Fenton s reagent and persulphates that involve the formation of free radicals. The percentage removal of the BTEX is about 98, 91 and 93% for the acidic, neutral and basic media respectively. The attack of PAH and BTEX were better at acidic ph, though the four ringed PAHs like benzoanthracene and chrysene were seriously attacked at all phs by the oxidant. Key words: Potassium permanganate, PAH, BTEX, TPH, chemical oxidant, hydrocarbon. INTRODUCTION Permanganates are crystalline solids well known as oxidizing agents. They are available as sodium and potassium permanganates. It is easily handled, readily available, strong and versatile oxidizing agent with a relative oxidizing power of Their versatility in reacting with a wide range of organic compounds over a wide range of ph is attributable to the variable oxidation state of manganese in the reactions at different phs (Nelson et al., 2001; Karpenko et al., 2009). At very acidic phs i.e at phs less than 3.5, they have been found to react as follows: MnO H + + 5e - Mn H 2 O In this, manganese has been reduced from manganate (VII) to manganate (II). At ph , which is the common environmental condition, the reaction is as follows: MnO H 2 O + 3e - MnO 2 + 4OH - Here, manganese has been reduced from oxidation number of seven to four. The manganese dioxide solid produced does not pose so much environmental problem for they occur naturally in soils. A good look at the reactions above shows that permanganate oxidation involves primarily electron transfer unlike the Fenton s reaction and the persulfate reactions that also involve free radical reaction (Ojinnaka et al., 2011, 2012). Their oxidation of organic compounds ultimately leads to such products as water, carbon dioxide, manganese dioxide and some oxygenated compounds especially organic acids as intermediates. *Corresponding author. Ozioma.achugasim@uniport.edu.ng. Te.: R + MnO 4 - MnO 2 + CO 2 or R ox

2 Achugasim et al. 5 Table 1. BTEX concentrations of the extracted oil before treatment with the potassium permanganate. BTEX Amount (mg/kg) Benzene Toluene Ethylbenzene P,M-xylene O-Xylene Where R =hydrocarbon and R ox = oxidized intermediate organic compound(gates et al., 2001). They have been found to be of good use in the management of organic pollutants in soils. A very good example of these organic pollutants is hydrocarbons. Permanganates have strong affinity for pie electrons of the carbon- carbon or carbon oxygen double bonds to form hypomanganatediester. This intermediate being very unstable reacts further in a number of steps that includes cleavage, hydroxylation, hydrolysis etc to give the final products which are carbon dioxide, water and manganese dioxide at the usual environmental ph of (Siegrist et al., 2001). Advantages of using permanganate over other chemical oxidants include; their reactions unlike Fenton reactions are not exothermic, ph control not an issue and catalysts are not required to drive the reaction. Also free radical scavengers such as carbonates are not required and being a mild oxidant, it can be used in association with bioremediation (Schroth et al., 2001). Permanganates have been successfully used in the oxidation of alkanes, alkenes, aromatic hydrocarbons, ketones, aldehydes, PAHs etc. (Damm et al., 2002 and Amanante, 2002). Bonny light crude oil is the most abundant crude oil type in Nigeria. It is sweet and light as the name suggests. The Niger Delta Province is heavily polluted with this crude oil type. Efforts and methods aimed at remediating the impacted soils have had little or no success. The need for other efficient remediation methods cannot be overemphasized in this part of the world. Gas chromatography (GC), an efficient tool in the study of hydrocarbon concentrations, is used in this study to evaluate the ability of potassium permanganate to remove petroleum hydrocarbons from crude oil polluted soils. MATERIALS AND METHODS Sandy soil samples (250 g) were weighed into three 1000 ml glass beakers. The phs of the samples were adjusted to acidic, neutral and basic using NaOH and HCl. The contents of the beakers were mixed with 20 ml of Bonny light crude oil sourced from Bomu oil Field in the Niger Delta area of southern Nigeria. The homogenized soil oil mixture in the containers were subsequently treated with 200 ml of potassium permanganate (KMnO 4 ) prepared by dissolving excess amount of the oxidant in water followed by filtration to remove undissolved particles. The treated samples were then taken to the laboratory for analysis together with an untreated sample that served as a control. The three hydrocarbons components mentioned above were all analyzed with a high resolution HRGC MEGA 2 series (FISONS instrument) Gas chromatograph (GC) equipped with a flame detector and the peak areas analyzed with an SRI model peak simple chromatography data system. A silica column of (30 m x 0.25 um x 25 mm) was used. TPH was analyzed at a column temperature of 60 C for 2 min to 300 C programmed at 12 C/min with nitrogen as the carrier gas. Hydrogen and air flow rate were 9psi and 13psi respectively. PAH was analyzed at a column temperature of 98 C for 1 min to 300 C programmed at 80 C/min and air flow rates were 12psi and 15psi respectively. BTEX was analysed at the initial temperature of 30 C for 1 min then increased to 180 C at 50 C/min and to 230 C at 20 C/min. Helium was used as the carrier gas. RESULT AND DISCUSSION The distribution of the various hydrocarbon groups (PAH, BTEX, TPH) of the untreated soil samples are shown in (Tables 1-3 and Figures 1-3). It can be clearly seen that removal of crude oil hydrocarbons from polluted soils using potassium permanganate is good and ph dependent with most of the depletions occurring at acidic medium (Figures 4-15 and Tables 4-6). It is also clear that the permanganate did not effect reasonable removal of the aliphatic hydrocarbons (TPH) but was good in the removal of the aromatic hydrocarbons. This could be attributed to the mode of reaction of the permanganates which is electron transfer unlike others that may involve formation of free radicals. Among the PAHs, removal at the acidic ph was better than the removal at the neutral or basic ph ranges. This is evident from Table 4 and Figure 7, as some of the PAHs were completely removed at the acidic ph. Generally the four- ringed PAHs such as pyrene, benzoanthracene and chrysene were seriously attacked at all ph ranges. Also the BTEX hydrocarbons were depleted by the treatment with permanganate. The depletion is also more pronounced at the acidic ph range. The percentage reduction of BTEX in the acidic medium is about 98%, 91% in the neutral medium and about 93% in the basic medium. This is shown in Figure 11 and Table 4. It is also clear that the treatment with permanganate resulted in the complete disappearance of the C 23 and above hydrocarbons at all ph ranges. Again this could be as a result of conversion of these longer chain aliphatic

3 6 Sky. J. Soil. Sci. Environ. Manage. Table 2. PAH distribution of the extracted oil before treatment with the potassium permanganate. Sample crude oil Amount (mg/kg) Sample crude OIL Amount (mg/kg) Acenaphthene(A1) Naphthalene(A7) Phenanthrene(A2) Chrysene(A12) Anthracene(A8) Fluorene(A9) Fluoranthene(A4) Dibenzothiophene(A13) Pyrene(A5) Acenaphthylene(A10) Benzanthracene(A6) Table 3. TPH concentrations of the extracted oil before treatment with the potassium permanganate. Sample crude Amount (mg/kg) Sample crude Amount (mg/kg) C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C Figure 1. BTEX fingerprints of the extracted oil before treatment with potassium permanganate.

4 Figure 2. PAH distribution of the extracted crude oil before treatment with the potassium permanganate. Achugasim et al. 7

5 8 Sky. J. Soil. Sci. Environ. Manage. Figure 3. TPH fingerprints of the oil extract before treatment with the potassium permanganate.

6 Achugasim et al. 9 Figure 4. PAH distribution of the soil sample after treatment with potassium permanganate at the acidic ph medium.

7 10 Sky. J. Soil. Sci. Environ. Manage. Figure 5. PAH distribution of the soil sample after treatment with potassium permanganate at the basic ph medium.

8 Achugasim et al. 11 Figure 6. PAH distribution of the soil sample after treatment with potassium permanganate at the neutral ph medium.

9 conc.(mg/kg) 12 Sky. J. Soil. Sci. Environ. Manage acid neutral basic un soil samples A PH AN FLU PY BEN NAP CH FLU DI AC Figure 7. Chart showing extent of depletion of PAH components of the sample after treatment with potassium permanganate at the various ph ranges. Figure 8. Chromatogram showing the BTEX fingerprints of the sample after treatment with potassium permanganate at the acidic medium.

10 Achugasim et al. 13 Figure 9. Chromatogram showing the BTEX fingerprints of the sample after treatment with potassium permanganate at the neutral medium.

11 Conc (mg/kg) 14 Sky. J. Soil. Sci. Environ. Manage. Figure 10. Chromatogram showing the BTEX fingerprints of the sample after treatment with potassium permanganate at the basic medium BENZENE TOLUENE ETHYLBENZENE P,M-XYLENE O-XYLENE 5 0 UNDEGRADED ACIDICSOIL SAMPLES BASIC NEUTRAL Figure 11. Chart showing the depletion of the BTEX components of the soil sample after treatment with potassium permanganate at the various ph ranges.

12 Achugasim et al. 15 Figure 12. Chromatogram showing the TPH fingerprints of the sample after treatment with potassium permanganate at the acidic medium.

13 16 Sky. J. Soil. Sci. Environ. Manage. Figure 13. Chromatogram showing the TPH fingerprints of the sample after treatment with potassium permanganate at the basic medium.

14 Achugasim et al. 17 Figure 14. Chromatogram showing the TPH fingerprints of the sample after treatment with potassium permanganate at the neutral medium.

15 Conc.(mg/kg) 18 Sky. J. Soil. Sci. Environ. Manage UNDEGRADED ACIDIC BASIC NEUTRAL SOIL SAMPLE C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 Figure 15. Chart showing extent of depletion of TPH component of the samples after treatment with potassium permanganate at the various ph ranges. Table 4. PAH distribution of the soil sample after treatment with potassium permanganate at different ph ranges. PAH(mg/kg) Acidic Neutral Basic Acenaphthene Phenanthrene Anthracene Fluoranthene Pyrene Benzanthracene Naphthalene Chrysene Fluorene Dibenzothiophene Acenaphthylene Table 5. Concentrations of the BTEX components of the sample after treatment with potassium permanganate at the different ph media. BTEX (mg/kg) Acidic Neutral Basic Benzene Toluene Ethylbenzene P,M-xylene O-xylene

16 Achugasim et al. 19 Table 6. Concentrations of the TPH components of the sample after treatment with potassium permanganate at the different ph media. SAMPLE mg/kg C 9 C 10 C 11 C 12 C 13 C 14 C 15 C 16 C 17 C 18 C 19 C 20 C 21 C 22 C 23 Acidic Basic Neutral hydrocarbons into shorter ones resulting in their disappearance. The depletion of the aliphatic hydrocarbons was almost the same at all ph ranges as can be seen from Table 5 and Figure 15. Conclusion This work has demonstrated that potassium permanganate can be used as a chemical oxidant in the management of crude oil polluted soils. The oxidant has been shown to be ph dependent when used in the remediation of crude oil polluted soils with acidic phs giving the highest hydrocarbon removal. Ojinnaka CM, Osuji LC, Achugasim O (2012). Remediation of hydrocarbons in crude oil contaminated soils using Fenton s reagent. Environ. Monit. Assess., 184(12): Ojinnaka CM, Osuji LC, Achugasim O (2011). Use of activated persulfates in the removal of of petroleum hydrocarbons from crude oil polluted soils. Res. J. Chem. Sci., 1(7): Schroth MH, Oostrom M, Wietsma TW and Istok JD(2001). Insitu Oxidation of Trichloroethane by Permanganate: Effects on Porous Media Hydraulic Properties. J. Contamination Hydrol., 50: Siegrist RL, Michael AU, Olivia RW, Mitchelle LC and Kathyn SL (2001). Principles and Practice of Insitu Chemical Oxidation Using Permanganate. Bettalle Press, Columbus Ohio REFERENCES Amanante D (2002). Applying in-situ chemical oxidation. Poll. Eng., 1: Damm JH, Christopher HR, Roberts MK and Kayleen PW (2002). Kinetics of oxidation of methyl tertiary butyl ether by potassium permanganate. Water Res., 36: Gates DD, Siegrist RL, Steven RC (2001). Comparism of Potassium Permanganate and Hydrogen Peroxide as Chemical Oxidants for Organically Contaminated Soils. J. Environ., Eng., 127(4): Karpenko O, Lubenets V, Karpenko E, Novikov V (2009). Chemical oxidants for remediation of contaminated soil and water. A review. Chem., Technol., 3 (1): Nelson MD, Parker BL, Torna A, Chery JA and Loomer D (2001). Geochemical reactions resulting from insitu oxidation of PCE-DNAPL by potassium permanganate in a sandy aquifer. Environ. Sci. Technol., 35(6):