MINERALOGICAL CHARACTERIZATION OF CALCINE, NEUTRAL-LEACH RESIDUE AND WEAK ACID-LEACH RESIDUE FROM VIEILLE-MONTAGNE ZINC PLANT, BALEN, BELGIUM

The roaster calcine, neutral-leach residue and weak acid-leach residue from the zinc operations of Vieille-Montagne, Balen, Belgium, were ch aracterized mineralogically to determine the forms of Fe, Al, As and S i that are present. The calcine consists principally of ZnO and ZnFe2O 4, which occur as rhythmically banded and porous grains, together with lesser amounts of Zn2SiO4, Zn-Fe-Pb silicate, sphalerite, quartz, PbS O4 and Fe2O3. Aluminium is present in solid solution in most of the ir on-bearing phases and also as residual aluminosilicate minerals from t he original concentrate. Silicon occurs mostly as Zn2SiO4, Zn- Fe-Pb s ilicate and as residual silicate minerals. Arsenic is commonly detecte d in the ZnFe2O4, Fe2O3 and Zn-Fe-Pb silicate phases. The major As car rier, however, may be <1-mum particles of calcium arsenate that are di spersed throughout the calcine. The neutral-leach residue consists mai nly of ZnFe2O4 and precipitated masses of iron gel-silica gel; lesser amounts of ZnO, Zn2SiO4, Zn-Fe-Pb silicate, PbSO4, sphalerite, Pb-K-ja rosite and basic zinc sulphate are also present. Aluminium occurs in m inor concentrations in most of the iron-bearing phases and in the Zn-F e-Pb silicate; the residual aluminosilicates are also an important Al carrier. The major As carrier is the precipitated iron gel-silica gel phase, but some As is also present in the Zn-Fe-Pb silicate, ZnFe2O4 a nd Fe2O3 phases. Silicon is divided about equally between the iron gel -silica gel, Zn2SiO4, Zn-Fe-Pb silicate and residual silicate minerals . The weak acid-leach residue is generally similar to the neutral-leac h residue except for its reduced content of ZnO and basic zinc sulphat e.