In the hydrometallurgical treatment of the zinc leach residue, arsenic in the zinc concentrate is condensed into iron precipitate such as hematite and goethite.
So it is difficult to utilize such iron precipitate as raw material for iron and/or its compounds.
From this point of view, the removal of arsenic from the leach solution prior to iron removalstage has been investigated means of corecipitation - with ferric hydroxide which is formed by oxidizing a part of Fe2+ion in the solution. The oxidation of Fe2+ ion was carried out by aeration under the coexistence of suitable amounts of calcium carbonate, using Denver type flotator.
Sample solution contained 69.8mg/l of As (III), 31.6g/1 of Fe2+, 60.7g/l of Zn2+and 162mg/l of Cd2+.The pH and temperature of the solution were 4.5 and 80°C, respectively.
The concentration of As (III) in the filtrate was reduced to 14 to 10mg/l by aeration for 10 min under the coexistence 2.5 to 5g/l of calcium carbonate and by filtration with No.5C paper filter. But, in this case the filtration rate was very and the filtrate was turbid. When filtration was repeated, the concentration of As (III) in the filtrate was reduced to to 1.2mg/l and the filtrate was transparent. The turbidity of the filtrate was remarkably reduced by using a polymeric flocculant, but the filtration rate was unchanged.When the solution was aerated for 10 min under the coexistence of a small amount of calcium carbonate (1g/l) and agitated for 10 min without aeration after adding 2 to 3g/l of calcium carbonate, the filtration characteristics were considerably imnroved and the concentration of As (III) in the filtrate was reduced to 6.0 to 1.5mg/l. If hernatite is precipitated from this filfrate its arsenic content will be 0.014 to 0.0035%. In this case, the loss of Fe2+, Zn2+and Cd2+was 5.4 to 6.5, 1.6 to 3.1 and 1.3 to 2.3%, respectively and the filtration rate was 2.1 to 2.3m3/m2/hr.
