Hemimorphite

As for the lead oxide ore types, there are a variety of zinc oxide ores. There are three basic ore types of economic value (a) ores with hemimorphite as the predominant zinc oxide minerals, (b) ores with smithsonite as dominant zinc oxide minerals and (c) ores with a mixture of smithsonite and willemite. Typical mineral compositions of this ore are shown in Table 20.1. 

Research work conducted at the University of Liege was carried out on several ore types that contained hemimorphite and smithsonite. The mercaptan-type collectors were effective with both minerals in the presence of sulphidizer. Although mercaptans floated oxide zinc minerals, the recoveries were not satisfactory. Later in the research work, amine-type collectors were introduced to flotation of oxide zinc minerals with significant improvement in metallurgy over that obtained with mercaptans. 

The combination of Na2S and amine was then introduced into the Gomo plant in 1954. The pH during flotation was found to be very important For flotation of calamine, the optimum pH was 10.5. In the presence of willemite-hemimorphite, the pH with RNH2 was about 11.5. The effect of pH on zinc oxide flotation in the presence of amine is illustrated in Figure 20.2. 

The zinc oxide ores of any economic value are represented by smithsonite and calamine. Willemite, franklinitc and other zinc oxide minerals are quite rare. The gangue minerals are usually represented by calcite ferooxides, dolomite and hemimorphite. The composition of gangue minerals, however, varies considerably and may also contain clay, talk, Fe-hydro-xide and other minerals. 

Structures containing this unit (Figure 1.52(b)) are not common but occur in thortveitite, Sc2Si207, and hemimorphite, Zn4(0H)2Si207. 

Disilicates or soro-silicates Discrete [Si207] units formed by two [Si04] tetrahedra sharing a common oxygen Thortveitite, Sc2(Si207) Hemimorphite, Zn4(0H)2(Si2O7)H2O... 

The rule reqiiires that in silicates the silicon tetrahedra share no elements with each other if the oxygen-silicon ratio is equal to or greater than four. This is found t o be vrue in general (topaz, zircon, olivine, other orthosilicates), Most of the few exceptional substances now known contain extra oxygen atoms in the form of hydroxide ions. These include the clay minerals, micas, and chlorites, discussed above, and also the mineral hemimorphite, Zn[Pg.561]

This structure is similar to those of the isoelectronic species P2074-, S2072-, and C1207 (the pyrophosphate and pyrosulfate ions, and dichlorine heptoxide). The minerals thortveitite, Sc2Si207, and hemimorphite, Zn4(0H)2Si207, contain the Si2076- unit, which has the structure shown earlier. 

Zinc is a blnish-white metallic element (symbol Zn atomic no. 30) that is found in minerals such as frankli-nite, ghanite, goslarite, hemimorphite, smithsonite. 

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