Acid Leaching for Metallic Impurities

Acid Leaching for bimetal ImpuritiesAcid Leaching for Metallic Impurities military rating of Some Mineral Ores in Nigeria*R.L. Tyohemba1 S. K. Emgba2AbstractThere is e actually need to access the impureness ratio of mineral ores in order to furnish investors and industrialists with training required to weigh the gains of venturing into their exploration. Metallic ores including Zinc ore (Sphalerite), compress ore (Magnetite), Iron ore (Heamatite), Copper ore (chalcocite), Lead ore (Galena) and gypsum were obtained from the bailiwick Geological Survey Kaduna. The ore samples were grounded and digested with aqua regia solution to leach their metal(prenominal) constituents using standard method. The main gilded components of the ores viz Zn, Fe, Cu, Pb and Ca were determined by the flame atomic absorption spectrophotometer (Biotech FAAS Phoenix 986) alongside their associated impurities. Galena (Lead ore) recorded the naughtyest gold-bearing impureness case of about 28.64 % a nd was followed by Sphalerite with about 6.31 % metallike impurities. The other ores recorded ZnMgNiPb. The impurity content of heamatite and magnetite were of the same trend in the order MnCuZnNiPb. However, heamatite recorded higher Fe content than magnetite. Galena contained 534.50 mg/Kg (71.36 %) deal content with its associated impurities usher in the order ZnMnCuCd. Sphalerite contained 8362.22 mg/Kg (93.69 %) as zinc while its associated impurities were present in the order of CuFeCaMnPb. In gypsum, its Calcium content was (97.15 %) with its associated gold-bearing impurities in the order MgFeKCrPb. The studied ores had a very high level of their major metallic constituents with unaccompanied Galena which had a high level of impurities. Thus these ores could be good feedstock to mine their principal components.1.1 INTRODUCTIONNigeria is abundantly endowed with a variety of mineral resources, fossil fuelsand solid minerals ranging from precious metals, various stones to industrial minerals such as Lead(Pb), Feldspar(xAl(Al,Si)3O8), ron magnetite(Fe3O4), iron hematite(Fe2O3), gypsum(CaSO4.2H2O),copper(Cu), Kaolinite(Al2O5(OH)4Si), Zinc(Zn), Limestone(caco3) e. t. c. Most of these be insofar to be exploited. Statistically, the level of exploitation of these minerals is very low in relation to the extent of deposits rig in the country. The presence of impurities in ores is inevitable due the reputation of their occurrence. Impurities in minerals may be caused by simple admixtures or by crystal chemical substitutions 1. Impurities are often responsible for colour changes. Natural impurities are common in minerals, as is the propensity for one element to slip into the crystalline structure in place of some other element. Exchanges of these forms do non cause a modification in mineral name as long as the replacements make up only a small property of the entire structure.Oxides nodules of Ni, Co and Cu have been found to occur in lattices of iron and manganese 2. Associated impurities of zinc(II) such as lead, iron, Copper, Silver etc., contained in are say to be found present in Nigerian sphalerite mineral3. The high manganese content of the sphaleritesleave them incongruous for processing by conventional smeltingtechniques, facilitating the inevitability to architectural plan and construct an onsiterefinery that is specifically suited for Gamsberg ores and concentrates 4. Naturally occurringsphalerite commonly incorporates variable concentrations ofimpurities (e.g. Fe, Cd, Mn, Cu, Co, Ni, Ge, In) that substitute zincin lattice sites. For example, FeS concentrations can range up to25 groin. %, while MnSseldom reaches up to 14 mol.%. Consequently,the high extent of stoichiometric inconsistency observedhas a marked effect on the processing, as high levels of theseimpurities in some zinc concentrates, i.e. Gamsberg, renders themunsuitable for processing by traditional operations.Copper is associated with tail endmetals suc h as family and cobalt.Studies have also been carried out on representative samples of Kre (Turkey) where massive rich copper ore were leached in blistering ferric sulfate solutions in order to recover copper and its associated metals (Zn, Co, Ni) present in the ore5.The minerals of lead and zinc are naturally associated with each opposite.In many split of the world, significant deposits of these mixed sulfideoxide lead and zinc ores are found with the main sulphideand/or oxidised ore bodies. Because of their complex mineralogy,these ores are very difficult to deal with from a mineral processing menstruum of view and they are very often left untreated as a result of themetallurgical difficulties encountered in extracting lead and zincfrom them. Although the primary sources of the metals are leadand zinc concentrates from sulphide and oxidised ores, as suppliesof these deplete, the processing of mixed ores must be considered6. Also, the lead-zinc ore from a mine is featured by co mplicated copper-lead-zinc intergrowth and uneven dissemination size. Besides, the minerals containing copper trigger by nature the mineral containing zinc, causing difficulty of separation of copper, lead and zinc minerals 7.There also published data on the presence of metallic impurities including Fe, Se, Mg, Al, Si, Cu, Zn, Pb, Cr, La, Ce, Nd and Y which were removed from desulpurized gypsum 8.Hayward and Quincy 9 developed a method for the treatment of iron ores containing impurities such as aluminium, silicon, chromium, nickel and cobalt from iron ores of the type which contain nickel in otiose of 0.25% and chromium in excess of 0.5%, such as for example those ores found in Cuba known as Mayari ores. The impurities which are present in all iron ores such as sulphur, phosphorus, manganese and silicon appear in iron and steel made there from. Such impurities are loosely undesirable in iron alloys, but it has not been possible to remove them completely, and only high phase iron ores are used at present in the production of iron. For this reason, various low grade iron ores have been wholly rejected, either because of their high contents of the impurities mentioned or because they contain varying amounts of base metals 10. These bulks of impurities mentioned in the essay have obvious unattractive characteristics that will increase the cost of mineral processing.There exist speculations that mineral ores in Nigeria are characterized by high levels of impurities. It then becomes imperative to access these mineral ores and their impurity ratios to furnish investors and industrialists with information that will help to estimate cost of production as wellhead as to find suitable methods applicable for their purification.2.1 METHODOLOGY2.1.1 Sample Collection and PreparationMineral ores including Zinc ore (Sphalerite ZnS), Iron ore (Magnetite Fe3O4), Iron ore (Heamatite (Fe2O3)), Copper ore (chalcocite Cu2S)), and Lead (Galena-PbS) were obtained from the N ational Geological Survey Kaduna. The samples were stored in the laboratory for the study. The ore samples were grounded using a porcelain mortar and pistol sieved and digested to leach their metallic constituents using the procedure described below.2.1.2 Acid remove of ore samples for metallic content determination.This was carried out as described by the ISO (1998)procedure 11. 1g of the grounded air dried ore sample was transferred into a 250 ml reaction vessel (Teflon digestion bomb). 10ml of the mixture of azotic acid and hydrochloric acid in a ration of 13 (aqua regia) was added unto the reaction vessel containing 1g of dried sample and heated using hot plate inside a fume hood until white fume was observed and allowed to cool.The reaction vessel was allowed to stand so that most of any insoluble balance settles out of suspension. The relatively sediment-free extract was decanted carefully onto a filter paper, collecting the filtrate in a 100 ml volumetric flask. All the si gn filtrate was allowed to pass through the filter paper, and the insoluble residue was washed onto the filter paper with a minimum amount of nitric acid (0.5 mol/l). The filtrate so collected was collected alongside the initial filtrate and the volume of the flask was made up to mark with deionized water supply. The extract thus alert was ready for the determination of the studied metals, by an atomic absorption spectrometer (Biotech FAAS Phoenix 986).3.1 RESULTS AND DISCUSSION3.1.1 Metallic Content of Copper Ore (Chalcocite).The result of metallic content of copper ore is presented in table 1. The concentration of copper in the ore was found to be 10341.73 (mgkg-1) representing about 97.7% of its metallic content covered by this work. Other metallic constituents which are considered to be impurities were also found present. Hence, Ca (99.65 (mgkg-1), Mg (63.89 mgkg-1), Ni (9.38 mgkg-1), Pb (1.99 mgkg-1) and Zn (73.26 mgkg-1) in the order CaZnMgNiPb. These metallic ions exists in their +2 oxidisation states as copper and could replace the Cu2+ in its lattice sites. In a similar work by 5, massive rich copper ore was leached in acidic ferric sulphate solutions and was able to recover copper and its associated metals (Zn, Co and Ni).Table 1 Metallic content of Copper ore (mg/Kg)3.1. 2. Metallic content of the studied Iron ores (Heamatite and Magnetite)Presented in table 2 are the available metallic contents of the studied iron ores. The mount of iron in the heamatite ore was found to be 6488.19 mgkg-1, representing (97.3) % of the core metallic content evaluated in the study. The iron content of magnetite was 5571.81 mgkg-1, representing 96.99%. However, an interesting trend was observed in the variation in the amount of metallic impurities which were found present in these iron ores. Both heamatite and magnetite varied in their level of impurities in the order MnCuZnNiPb. Oxides nodules of Ni, Co and Cu have been found elsewhere to occur in lattices of iro n and manganese ores 2. Hayward and Quincy 9 had already identified impurities such as Aluminium, Silicon, Chromium, Nickel and cobalt from iron ores of the type which contained nickel in excess of 0.25%. The values reported in this study for both iron ores are lower in nickel content than those recorded above (0.21 and 0.18) % nickel for heamatite and magnetite respectively.As earlier stated in literature, iron alloys are generally undesirable but it has not been possible to remove them completely, and only high grade iron ores are used at present in the production of iron. For this reason, various low grade iron ores have been wholly rejected, either because of their high contents of the impurities mentioned or because they contain varying amounts of base metals 10. From the results presented in this study, Nigerian iron ores are of high iron content with very minimal impurity content in the ratio of (135 and 132) iron to metallic impurities content of heamatite and magnetite.Tabl e 2 Metallic content of iron ores (HeamatiteMagnetite) (mg/Kg)**H Heamatite **M Magnetite3.1. 3 Metallic Content of Lead Ore (Galena)The recorded amount of Pb in the galena ore was 534.50 mgkg-1, representing (71.36) % Pb content of the studied metallic components. Also, other metallic components considered to be impurities including Cadmium, Copper, manganese and Zinc were found present in the ore as presented in table 4 in the order ZnMnCuCd. The metallic impurities of Zn and Mn were present in relatively large amounts. (i.e. 14.21 and 12.85) %. The minerals of Lead and zinc are naturally associated with each other. In many parts of the world, significant deposits of these mixed sulphide-oxide lead and zinc ores are found with the main sulphide and/or oxidized ore bodies. Because of their complex mineralogy, these are very difficult to deal with from mineral processing point of view and they are very often left untreated as a result of the metallurgical difficulties encountered i n extracting lead and zinc from them 6.Table 4. Metallic content of Lead ore (mg/Kg)3.1.4 Metallic Content of Zinc ore(Sphalerite)The results are found in table 5. Zinc content was determined to be 8362.22 mgkg-1 (93.69) % of the ores metallic content studied. Other metallic components which are considered to be common impurities associated with zinc ores were also found present in the other CuFeCaMnPb. The occurrence of zinc with such impurities has earlier been reported in the previous session.Table 5. Metallic content of Zinc ore (mg/Kg)3.1.5 Metallic content of gypsumHeiska (2011) have reported the presence of metallic impurities including Fe, Se, Mg, Al, Si, Cu, Zn, Pb, Cr, La, Ce, Nd and Y in gypsum. As presented in table 6, the main metallic component of gypsum which is calcium was evaluated to be 9921.03 mgkg-1, representing 97.15 % of the tote up metallic content of the studied metals. Other metals such as Cr, Fe, Mg, K and Pb were found present in the acid leached mineral in the order MgFeKCrPb. The dominance of Mg as an impurity in this ore is much expected as the metal ion (Mg2+) is known to occur in areas where there calcium deposits exchanging at its lattice and together causing water hardness.Table 6. Metallic content of Gypsum ore (mg/Kg)3.1.6 Main metal component and impurities ratios of studied oresIn table 7 and fig. 2, the summary of these ratios are presented. Lead ore had the highest level of total metallic impurities recording about 28.69 % as impurities in its ore. Others had low metallic impurities in them. Zinc ore recorded less than 10 % as metallic impurities. On the other hand, metallic impurities in copper, heamatite, magnetite and gypsum were less than 5 %.Table 7.Metal/metallic impurity ratios of studied ores.Fig.2 Metal/metallic impurity ratios of studied ores4.1. inferenceThe analysis of metallic content of some of the Nigerian mineral ores presented from the result indicates that the studied metallic ores are rich in their principal metallic constituent. The only exception observed is the high impurity content of galena (Lead ore). All the other mineral ores had a little percentage of metallic impurities in them. It is gain reflection that these raw materials could serve as very rich industrial feedstock that will require little processing and thus serve cost. 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