Recovery of zircon from Sattankulam deposit in India problems and prospects

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1 MURTY, V.G.K., UPADHYAY, R., AND ASOKAN, S. Recovery of zircon from Sattankulam deposit in India problems and prospects. The 6th International Heavy Minerals Conference Back to Basics, The Southern African Institute of Mining and Metallurgy, Recovery of zircon from Sattankulam deposit in India problems and prospects CH. V.G.K. MURTY*, R. UPADHYAY*, and S. ASOKAN* Titania Business Unit, Tata Steel, Chennai, India (ZrSiO 4 ) is the most frequently found zirconium ore occurring in heavy mineral sands, from which it is extracted as a co-product in the production of ilmenite and rutile. Estimated world reserves of zircon are 124 million tonnes, highest in Australia (around 56 million tonnes), followed by Mozambique (15 million tonnes), India (12.6 million tonnes) and South Africa (12 million tonnes). finds its application in ceramics (54%) and refractory industries (14%), which account for 68% of zircon s total world consumption of 1.20 million tonnes. The rest (32%) is consumed in foundry, TV glass, zirconia chemicals and other applications. It is a long recognized feature of the zircon industry that supply is totally dependent upon the concurrent production of titanium minerals. But in recent years, several new developments such as the discovery of zircon-rich mineral sands in Australia, the continuing trend of higher prices of zircon and increase in trade of lower quality zircon have changed the scenario. These factors have prompted more intensive efforts to increase the recovery of zircon, particularly in the process for separating zircon from alumino-silicate minerals. Tata Steel s proposed heavy mineral sands deposit contains on an average 10% heavy mineral content and 15% slimes of the size below 63 micron. Mineral assemblages of the resource contain 65 70% ilmenite, 4 6% rutile, 4% zircon, 16% sillimanite and other minor minerals. Wide size range and tenacious iron oxide coating are the inherent characteristics of this deposit. High concentration of sillimanite among the non-magnetic heavy minerals and heavy surface coatings on the minerals are challenges for high recoveries and production of premium grade zircon. This paper outlines various process steps that were taken at pilot plant stage to produce zircon of premium grade and subsequently develop the appropriate flow-sheet. Introduction (ZrSiO 4 ) is the most frequently occurring mineral for the element, zirconium (Zr). It is a common accessory mineral in granitic rocks and pegmatites and, because it is highly resistant to mechanical and chemical disintegration, it most commonly occurs as a detrital mineral in river and beach sands 1. While zircon is a common accessory mineral, it is generally not found in high concentrations other than in placer and dune deposits, where it has been deposited along with other heavy minerals such as ilmenite, rutile, monazite, garnet, staurolite and kyanite. Such deposits have been sorted and concentrated over geological time by the action of tides, waves and wind to form concentrated deposits of heavy minerals along old coastlines and in river beds and deltas. It is these secondary concentrations of zircon in placer deposits that provide the only commercial sources of zircon. Consequently, zircon is always found in association with principal titanium minerals, ilmenite and rutile. The proportion of zircon in such heavy mineral deposits varies widely, depending upon the original concentration of zircon in the source rocks. is by far the most common source of zirconium, but the element also occurs in a number of other minerals, either as an oxide or as a silicate. The most common zirconium-containing minerals are shown in Table I. Apart from zircon, the only zirconium mineral currently of commercial significance is baddeleyite, which contains predominantly zirconia (ZrO 2 ) with some associated hafnium and is produced from a single source at Kovdaor, Russia. is produced mainly from heavy mineral sands mining operations, from which it is extracted as a coproduct in the production of ilmenite and rutile. Estimated world reserves of zircon are 124 million tonnes, highest in Australia (around 56 million tonnes), followed by Mozambique (15 million tonnes), India (12.6 million tonnes) and South Africa (12 million tonnes) 1. finds Table I Minerals containing zirconium Mineral Composition ZrO 2, weight % Baddeleyite ZrO Catapleite (Na 3 Ca)ZrSiO 3 O 9.2H 2 O Elpidite Na 2 (Zr,Ti)Si 6 O 15.3H 2 O Eudialyte-eucolite (Ca,Na) 5 Zr 5 Si 6 (O,OH,Cl) Polymignite (Ca,Fe,Y,Zr)(Nb,Ta,Ti)O Rosenbuschite (Ca,Na) 3 (Zr,Ti)Si 2 O 8 F Tazheranite CaTiZrO Wohlerite NaCa 2 (Zr,Nb)Si 2 O 8 (O,OH,F) ZrSiO Zirkelite (Ca,Fe)Zr,TiO RECOVERY OF ZIRCON FROM SATTANKULAM DEPOSIT IN INDIA PROBLEMS AND PROSPECTS 69

2 its application in ceramics (54 %) and refractory industries (14 %), which account for 68% of zircon s total world consumption of 1.20 million tonnes per annum. The rest (32%) is consumed in foundry, TV glass, zirconia chemicals and other applications. Tata Steel s proposed Titania project covers a part of the inland and coastal deposit of Tamil Nadu state in India, which expends over an area of about 200 sq. km along the coast. Tata s area of interest consists of two sand concentrations that cover approximately 120 sq. km. along the coast and inland, referred to locally as the Teri Lands. Tata Steel has applied for mineral licences on these two deposits, referred to as Sattankulam and Kuttam respectively, as shown in Figure 1. Outokumpu-PAH-L&T consortium acted as the feasibility study consultants and M.N.Dastur & Company as the infrastructure consultants for carrying out the bankable feasibility study. TZ Minerals International was appointed as the process and marketing consultant to ensure the feasibility study progressed as per the intended purposes. The sand contains heavy minerals that include ilmenite, rutile, zircon, sillimanite, monazite, magnetite and other minor minerals. The average total heavy minerals (THM) and slime (below 63 microns) content within the deposit is 10% and 15% respectively. Heavy minerals are concentrated in the micron size fraction. Mineral assemblages of the resource contain 65 70% ilmenite, 4 6% rutile, 4% zircon, 16% sillimanite and other minor minerals. After mining, the ore is subjected to beneficiation process, which involves a wet primary concentration and a dry mineral separation. The primary concentration plant (PCP) upgrades the run of mine (ROM) ore by rejecting light gangue materials such as quartz and shells to produce a heavy mineral concentrate (HMC) containing >95% HM with minimum losses of valuable heavy minerals (VHM) such as ilmenite, rutile and zircon. After separation of ilmenite and rutile through magnetic and high tension (HT) separators, the rest of the HMC is subjected to zircon recovery processes. Typical mineralogical analysis of feed to the zircon circuit and that of HMC from a bulk sample is shown in Table II. Challenges in recovery of premium grade zircon There is a continuing challenge to achieve higher product recoveries from ever more difficult mineral suites, with more consistent and predictable product quality. There is a particular focus at the present time on achieving higher recovery of zircon to satisfy growing demand of 3.0% per year 1. This challenge becomes more compounded when the endeavour is to produce premium grade zircon. Iron (Fe 2 O 3 ) content is often the most limiting specification in determining the suitability of a zircon product for a particular application. In particular, low Fe 2 O 3 content is often requested for ceramic opacifier applications. Iron content is controlled principally through grain surface cleaning and efficient mineral separation, minimizing contamination by leucoxene and staurolite. 1 Table II Typical mineralogical analysis of HMC and feed to zircon circuit Mineral Weight % in feed to Weight % in HMC zircon circuit Ilmenite Rutile Monazite Sillimanite Others Total heavy minerals Figure 1. Location of Tata Steel s titania project 70 HEAVY MINERALS 2007

3 The next limiting factor is Al 2 O 3. High Al 2 O 3 contents are normally an indication of contamination by aluminosilicate minerals, typically kyanite or sillimanite. While these minerals can be effectively separated from zircon using wet or dry gravity separation techniques, the presence of corundum would make the separation complicated. The low radioactivity of the zircon is important to zirconium/zirconia producers, who must deal with the elevation of radiation in waste streams. The level of U+Th in a zircon product may be influenced by particles of monazite, which may be removed by magnetic separation and wet and dry gravity separation process at the cost of recoveries. However, in most clean zircon products, the U+Th content is a function of the extent to which these elements are present in the zircon crystal structure, and this U+Th cannot be removed by physical processing methods. Therefore, maintaining U+Th levels of below 500 ppm in the zircon product without losing much in recoveries normally pose serious challenges to zircon producers. The presence of undesired minerals such as sillimanite, kaolin, corundum and monazite coupled with iron oxide coatings poses formidable challenges in the production of zircon of premium grade for ceramic applications. The critical quality parameters for premium grade zircon are given in Table III. In production of premium grade zircon, rejection of sillimanite from the zircon stream has always been the biggest challenge due to the small specific gravity difference between zircon (4.6) and sillimanite (3.25) and the stringent limit on alumina content, i.e., 0.45% in premium grade zircon. Microscopic images of original zircon in ROM sand and pure zircon mineral produced from the Sattankulam deposit are shown in Figure 2A and Figure 2B. From these photographs, one can see how white transparent grains of zircon are coated with heavy tenacious iron oxide coatings (which are deep and hard to remove) and interstitial iron staining. Without removal of these coatings, specifications of premium grade zircon (with respect to iron oxide content) cannot be met. Such heavy iron oxide coatings and the presence of sillimanite are major challenges in the production of premium grade zircon from Sattankulam deposit and call for detailed studies for arriving at the most efficient process route to produce zircon of premium grade. Industry practice for zircon recovery Traditionally in the mineral sands industry, after removal of magnetic and conducting minerals, viz., ilmenite, rutile, monazite and garnet, HMC now rich in non-conducting and non-magnetic minerals, is fed to the zircon circuit. In general, for simple deposits without any coatings, the wet gravity circuit is followed by the dry mill. In the wet gravity circuit, sillimanite and quartz are removed from zircon, thereby producing zircon concentrate. After drying the zircon concentrate, it is subjected to HT and magnetic separation to remove traces of magnetic and conducting minerals. However, surface stained zircon concentrates are cleaned in high energy input attrition cells using a neutral, acid, or basic solution. While this approach is found to be suitable for mildly stained grains, for more strenuous coatings, special chemical processes are used for removing coatings from the surface of zircon grains. These are the 1 : Hot acid leach (HAL) process, in which hot zircon is treated with moderately concentrated sulphuric acid and reacted in a kiln, after which the product is attritioned, neutralized and dried. A variant of this process employs a plug flow reactor in place of the rotary kiln upgrading process (ZUP), which involves heating the zircon to around 400 C, after which it is quenched in dilute sulphuric acid. To quantify performance of various surface cleaning techniques on primary zircon concentrates, tests conducted elsewhere revealed that conventional attritioning was able to reduce ferric oxide level from 1.02% to %, whereas by using HAL it can be reduced to a level of 0.29 %. 2 Figure 2A. Coated zircon in ROM sand Table III Quality specification of premium grade zircon Constituent Weight % ZrO 2 +HfO 2 Min. 66 TiO 2 Max Al 2 O 3 Max Fe 2 O 3 Max SiO U+Th (ppm) Max. 500 Figure 2B. Pure zircon mineral RECOVERY OF ZIRCON FROM SATTANKULAM DEPOSIT IN INDIA PROBLEMS AND PROSPECTS 71

4 The list of major zircon producers is given in Table IV. From the same, it is evident that major zircon producers have hot acid leaching facilities in their zircon circuit. It is observed that deposits with a higher proportion of slimes have coatings problems and, hence, require hot acid leaching facilities. Pilot plant test work for zircon recovery 4 During the feasibility study for Tata Steel s Titania project, the non-conductors and non-mags from the rutile separation process were used as feed to the zircon circuit for the pilot plant test work. The flowsheet of pilot plant for zircon circuit is shown in Figure 3. The feed first reports to a Floatex density separator for classification prior to the Wilfley table. The Wilfley table was used instead of spirals due to the limited sample size at this stage of the flowsheet. The concentrates from the Wilfley tables were combined and scrubbed to remove any surface coatings. As for the choice of reagent for attrition scrubbing, sulphuric acid has been found most effective for primary scrubbing and for secondary scrubbing; both acidic and alkaline reagents were found to work quite similarly. The zircon circuit being at the end of the MSP process, it was decided to do an alkaline scrub rather than an acid scrub in view of possible oil and carbon contamination. Therefore, slaked lime was used for scrubbing. Table IV List of major zircon producers 3 and the acid leaching facilities Producer Country Hot acid leaching facility production in 2005 ( 000 tonnes) Bemax Resources NL Australia No 20 Consolidated Rutile Limited Australia No 53 Doral Mineral Sand Pty Ltd Australia No 16 EI Dupont de Nemours & Co Inc USA Calcining only 65 Iluka Resources Limited Australia/USA Yes 365 Indian Rare Earths India No 22 Industrias Nucleares do Brasil Brasil No 5 Millennium Chemicals do Brasil Brasil No 20 Minerals and Trading Company (MITRACO) Vietnam No 8 Namakwa Sands South Africa Yes 129 Richards Bay Minerals South Africa Yes (calcining) 235 Ticor South Africa Yes 47 Corridor Sands (proposed) Mozambique Yes 30 Moma (Proposed) Mozambique Yes 60 Tiwest Joint Venture Australia No 70 Vilnohrisk State Mining and Metallurgical Plant Ukraine No 30 Non-cond product feed to zircon cicuit Underflow Floatex density separator Overflow Wilfley shaking table Wilfley shaking table NaOH Scrub Non-cond eforce HTR Cond Non-cond eforce HTR Con to rutile Non-cond 5-P ES Plate Cond Non-mag zircon RER Non-mag Mag RER Mag eforce HTR Cond Non--cond zircon Figure 3. pilot plant flowsheet 72 HEAVY MINERALS 2007

5 Table V Chemical analysis of zircon products before scrubbing Product Weight % %TiO 2 %ZrO 2 Dist. TiO 2 Dist ZrO 2 Feed No. 1 zircon No. 2 zircon No. 3 zircon Total zircon Conductor to rutile circuit Sillimanite feed Tails from table After scrubbing, desliming and drying, the material was subjected to HT separation. The conductors from the initial stage were scavenged on an additional stage of high tension roll (HTR) separator. The non-conductors from the scavenging stage were combined with the middlings from the initial HTR stage and treated on an ES plate separator. The non-conductors from both stages were combined and reported to a three-stage rare earth roll (RER) magnetic separator with the non-magnetic product from this stage being the primary zircon product. The magnetic product was then subjected to a scavenging stage on another threepass RER to recover any remaining zircon. The nonmagnetic product was then cleaned on an HTR separator. In order to further increase the recovery of zircon, the magnetic reject from the scavenger magnet was again treated on another three-stage RER and the non-magnetic product so derived as a secondary product contained slightly higher TiO 2 values. Within the zircon process flowsheet, three different zircon products were produced ranging from a high grade zircon to zircon of lower grades. Chemical analysis and the proportion of products are given in Table V. Table V shows that a total of 65.81% of the total zircon was recovered in three separate products of various grades with the majority (47.96%) recovered as the No.1 zircon product. Of the losses, the single largest stream was the tailing stream from tables accounting for 15.76% of the zircon or 69.9% of the losses. The material was coarse, because the zircon was treated on wet tables. Wet tables inherently recover fine material in preference to coarse mineral. This material was treated on a Kelsey jig to improve zircon recovery. Analysis of Kelsey jig concentrate 5 revealed that it contains 1.51% alumina (Table VI), which is higher than the specification. To reduce it further, Kelsey jig concentrate was treated on wet tables. Detailed analysis of zircon recovered from different process routes revealed Fe 2 O 3 content of more than 0.16% Table VI Analysis of Kelsey jig test Constituent Weight % ZrO 2 +HfO Concentrate assays TiO Fe 2 O Al 2 O which is well beyond specification of 0.10% for premium grade zircon. It showed that even the treatment with slaked lime was not able to keep Fe 2 O 3 within limits and therefore, required hot acid leaching. Having realized that hot acid leaching is essential to reduce iron oxide to an acceptable level, the question remained about the ideal location of hot acid leaching in the flowsheet. The various locations of hot acid leaching in the rutile/zircon circuit were anticipated to affect differently the recovery as well as the quality of rutile and zircon products, besides operating and capital costs. Hence, the following four options were tested to decide the best option (Table VII). The determination was based on single pass HT separation efficiency. Since the presence of quartz was expected to interfere with the operation of HT separation, it necessitated going for wet gravity concentration (WGC) prior to HAL/HT. This will not only improve separation efficiency of HT separators but also reduce the quantity of material to be redried. The combination of Floatex and wet gravity circuit vis-à-vis the use of the Kelsey jig ahead of the HT circuit was also studied for efficient recovery of zircon and rutile. Therefore it was decided to test only options 3 and 4. For hot acid leaching, the material was heated to 150 C, then moistened with 40% H 2 SO 4 solution and left for digestion in a refractory lined vessel for 30 minutes. After digestion, zircon was quenched in water, counter currently washed, dewatered and dried. Table VII Hot acid leaching various location options in zircon flowsheet Sl. No. Option Advantage Disadvantage 1 HAL-HT-Gravity Dry feed, 100% chances to recover in Higher costs since 100% through acid leach HT, highest recovery 2 HAL-WGC-HT Drying of zircon once Potential loss of leucoxene. Impact of loss of leucoxene on zircon quality 3 WGC-HAL-HT Lower HAL tonnages, HT advantage 2 times drying 4 Crude zircon product-hal Lowest volume through HAL, May not clean up grains enough to get best HT (WGC-HT-HAL) least likely to mobilize radio nuclides from monazite and mag. sep results for rutile and leucoxene recovery RECOVERY OF ZIRCON FROM SATTANKULAM DEPOSIT IN INDIA PROBLEMS AND PROSPECTS 73

6 Though HT separation efficiency (Table VIII) in the case of option 3 (WGC-HAL-HT) was higher than that in option 4 (WGC-HT-HAL), the difference was only marginal and within analytical errors. Finally, option 4 was selected as it will also give a cost advantage. Based on the decision to subject the crude zircon product from the HT separation to hot acid leaching, zircon product produced from pilot plant was hot acid leached. Analysis of zircon product before and after HAL treatment (Table IX) revealed that hot acid leaching of zircon product is effective in reducing the iron oxide content to below 0.07 % resulting in a premium grade zircon. Microphotographs of zircon in non-mag and the zircon product after hot acid leaching (Figure 4) clearly indicate the significant drop in iron oxide level 6. The brownish colour of zircon particles (Figure 4A) is due to heavy coatings of iron oxide and the same is conspicuous by its absence in the final product (Figure 4B). (a) in Non Mag. Reflected light Coating on Conclusion is the most frequently found zirconium ore and is produced mainly from heavy mineral sands mining operations, from which it is extracted as a co-product in the production of ilmenite and rutile. A high proportion of sillimanite among the non-magnetic heavy minerals, heavy iron oxide surface coatings on the zircon mineral and the presence of monazite are major constraints for high recoveries and production of premium grade zircon in the case of the Sattankulam deposit in India. The combination of a conventional wet gravity circuit and dry separation employing electrostatic and magnetic separators is not able to produce premium grade zircon, necessitating the introduction of a hot acid leaching facility in the circuit. Various permutations and combinations were tried to decide on the location of the hot acid leaching circuit, and hot acid leaching of crude zircon concentrate was found to be the best among all the options tried for producing premium grade zircon economically. Acknowledgements The authors would like to express their thanks to their colleagues in the Titania Business Unit for their help in preparing the paper and Tata Steel for the constant Table VIII Comparison of HT separation efficiency with and w/o HAL Options Separation efficiency(tio 2 /ZrO 2 ) % WGC+HAL+HT (3) 89.4 WGC+HT+HAL (4) 88.5 Table IX Analysis of zircon products before and after HAL Compound Feed to zircon circuit, product, weight% weight% Before HAL After HAL ZrO 2 +HfO TiO Al 2 O Fe 2 O (b)washed zircon Reflected light Figure 4. Microphotographs of zircon particles in non-mag and in final zircon product encouragement and support provided. The authors also would like to express their gratitude to Mr D.S. Rao of the National Metallurgical Laboratory, Chennai, India for his assistance in preparing microphotographs of various products. References 1. TZ MINERALS INTERNATIONAL PTY. LTD., The Global Industry, New era new dynamics, pp LAYVENDER, M.D. and JAMES, D.G. Production of high quality zircon using the H.A.L.process, 10th Industrial Minerals International Congress. 3. TZ MINERALS INTERNATIONAL PTY LTD., Mineral Sands Annual Review pp OUTOKUMPU TECHNOLOGY, Feasibility Study Test Results. Private Communication, ROCHE (MT), Kelsey Jig Test Report, Private communication, OUTOKUMPU TECHNOLOGY, Mineralogical analysis. Private communication, HEAVY MINERALS 2007