Preparation of high purity cadmium with micro-spherical architecture from zinc flue dust
(School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: This research has focused on the treatment of zinc flue dust by an acid leach process, combining an environmentally suitable impurity removal process to recover cadmium. Optimum conditions were found as follows: H2SO4 concentration 90 g/L, liquid/solid ratio 6:1, leaching temperature 60 °C and leaching time 1.0 h. Under these conditions, 95.8% cadmium was recovered. FeAsO4 and Fe(OH) 3 precipitates with FeCl3 are found to be highly effective to obtain a high degree of separation of heavy metals and the oxyanions of arsenic from the leachate. The overall separation of arsenic and other heavy metals and precipitate settling rates are optimum at n(Fe)/n(As) ratio of 3:1 and pH 6. The removal rates of Fe, Pb and Cu from the solution were greater than 98.9%, and As removal rate was 99.6%. A solvent extraction with P204 was used for the separation of zinc and cadmium. Optimum conditions are obtained as follows: 20% P204 (volume fraction) diluted with kerosene at room temperature, pH 3.0, and varying organic/aqueous (O/A) phase ratio 1:1. The extraction rate of zinc is 99.2% under these conditions. Spherical cadmium particles showing nearly uniform size were produced by hydrogen reduction at 310 °C and the crystal structure was cubic. In addition, the purity of the recovered cadmium powder is more than 99.99%.
Key words: zinc flue dust; impurity removal; micro-spherical; cadmium powder