| Base metals such as cobalt, zinc and copper are present in African copper smelter slag during the pyrometallurgy process, it is very important for economy and environmental protection to recover these metals, the theory was studied in detail in mineralogy, thermodynamics and so on in this paper, a flowsheet to recover cobalt, znic and copper in the slag was presented, which is "Selective leaching slags—Effective refining and separating cobalt, zinc and copper".The main points and cotent of this paper are indicated as following:(1) The copper smelt slag assaying 4.087% cobalt,1.349% copper, 1.7% zinc,15.38% silicon and 28.43% iron is produced by pyrometallurgy operations. The slag is originated from Africa with character of high silicon and iron, meanwhile cobalt is rich in the slag, so it is economical to recovery cobalt from the slag.A feasible hydrometallurgical method for selective leaching at atmospheric pressure-neutralizing coagulation to recovery cobalt, zinc and copper in the slag was shown on this paper. Four key parameters, namely sulfuric acid addition, sodium chlorate amounts, reaction temperature and time, are examined on the process performance. Calcium hydroxide is chosen as the optimal neutralizer to coagulate silicon and iron ion during the coagulating stage without filtration. The reaction endpoint is defined. Via filtering and washing, Silica gel-free solutions and good filterable cakes are obtained. The optimum conditions for the maximum recovery of 20g copper smelt slag are determined as follows: with TC1,17.6g sulfuric acid as leaching agent; oxidant sodium chlorate 2.5g; reaction time 3 hours at 95℃, using calcium hydroxide 4.3g, reaction endpoint defined as pH maintains 2.0 for 1 hour at least. The cobalt maximum recovery efficiency of the method amounts to 98% nearly, while zinc and copper recovery efficiency is 97.3%,89.1%, and leaching efficiency of silicon and iron is only 3.2% and 0.02%, respectively.This study is not only a breakthrough the bottleneck of silica gel formation and pulp filtration, but also a good removal iron and silicon completely, and a filterable cake is obtained. Natrojarosite NaFe3(SO4)2(OH)6 and gypsum CaSO4·2H2O is a main component of the slime after leaching by X-ray analysis, while stishovite SiO2 is a reaction product during the coagulating process. Cobalt and zinc is hardly found in the residue. It indicates that the technique of oxidative leaching and coagulation has a perfect selectivity.(2) Aluminium is removed by hydrolysis precipitation method with NH4HCO3, the removal efficiency of aluminium reaches 100%, almostly, while the loss rate of cobalt is less than 0.33% and that of zinc, copper is less than 1.1%. Cobalt, zinc and copper are separated from calcium and magnesium by controlling pH to 7.5. Re-leaching the hydrolysis residue with acid, extracting copper by X1 and zinc by X2, respectively. CoC2O4·2H2O is prepared with (NH4)2C2O4·H2O. The recovery efficiency of cobalt, zinc and copper could be 94.7%,92.6%,85.7%, respectively.The recovery efficieny of base metals in this investigation is high, while this hydrometallurgical treatment without roasting has a perfect selectivity. The proposed procedure is operationally simple and economical with strong competitive power and may be applicable in the industrial recovery of base metals from copper smelt slag. |
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