Enhancing the recoveries and grades of Cobalt from Nchanga and Konkola Ores of KCM
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The Nchanga and Konkola ores have substantial amounts of cobalt in the form of Carrollite (CUC02S4) and Cobaltiferous pyrite ((Co,Fe),S2). These minerals are found in association with copper minerals such as chalcopyrite (CuFeSz), Bomite (CusFeS4) and Chalcocite (CujS). However, the recoveries of cobalt minerals in both Concentrators are low (45-50%TCo). In this work, a combination of the electrokinetic, Ultra-Violet spectrometry, X-ray Photoelectron spectrometry, contact angle measurements and micro-flotation techniques were used to characterise the optimal conditions for the improvement of recoveries and grades of cobalt mineral (Carrollite) without adversely affecting the recoveries and grades of copper minerals such as Chalcopyrite. The studies confirmed that in acidic media (pH 3 - 6), copper ions are easily leached into solution whereas cobalt ions are only leached at high pH values (9 -11) in the alkaline media. The zeta potentials of both Carrollite and chalcopyrite are negative throughout the pH range (3- 11). Charge reversals at pH 7.5 and pH 10.5 are achieved in oxygen saturated solutions for Carrollite mineral. Sodium Isopropyl Xanthate (SIPX) decomposes to xanthic acid at pH 3 whereas at high pH (> pH 6) a substantial amount of Xanthate ions is present due to ionisation of SIPX into metal cation and Xanthate anion. The adsorption of Xanthate ions on Carrollite minerals is rapid in the first 5 minutes of adsorption test work. A fresh Carrollite mineral sample has the following oxidation states for its elemental constituents; Cu (I), Co (III) and S (I The Carrollite mineral is fairly stable at pH 3 in water, SIPX and oxygen saturated solution. Cu(OH)2, CuS and CuX2 are formed at high pH values (pH 9 and 11). The formation of hydrophobic species is optimum at pH 9. The maximum contact angles (33.5° and 49.8") were achieved at pH 9 both for untreated and treated in SIPX polished sample respectively. This is confirmed in the high recoveries and grades achieved at pH 9 - 10.5. The outcome of the laboratory flotation tests work on the actual cobalt mineral and ores were that pH 9 gave better recoveries for SIPX (74.7% TCu and 71.8% TCo) and SIPX: PAX (Potassium Amyl Xanthate) (74.4% TCu and 78.3% TCo)as collectors respectively. These sets of results imply that:1. the loss of copper/cobalt minerals in aqueous solution is minimal as there is negligible amounts of dissolved metal ions in solution 2.the charge on the mineral surface in solution is influenced by pH and hence gives guidance to the type of collectors that easily adsorb and induce the required effect (activation or depression of the minerals of interest) on the mineral surface 3. the formation and precipitation of metal hydroxide on the mineral surface is detrimental to flotation whereas metal-deficient sulphide rich surfaces, metal sulphide and metal dixanthogen are responsible for flotation.
- Mines