Hot-acid leach

The principal differences between the goethite and the jarosite processes take place following the hot acid leaching of the zinc ferrite residues. In the goethite process, the liquor from hot acid leaching, holding (in g l-1) 100 Zn, 25-30 Fe3+ and 50-60 H2S04, is initially subjected to a reduction step, where the ferric iron is reduced to the ferrous form by reaction with unroasted zinc sulfide concentrate at 90 °C ... 

Iron-bearing solution from hot acid leaching... 

HAL [Hot acid leaching] A process for purifying silica sand or zircon by leaching out surface iron compounds with hot sulfuric acid. Derived from an earlier process, invented in 1955 by British Industrial Sand, in which silica sand was treated with hot, gaseous hydrogen chloride. The process for cleaning zircon sand was developed jointly by Hepworth Minerals Chemicals, UK, and Metallurgical Services Pty, Australia, in 1991. 

The roaster product is lcachcd with spent electrolyte 1 sulfuric acid) under near-neutral conditions to dissolve most of the zinc, copper, and cadmium, but little of the iron. The leach residue solids are releached in hot, strong add to dissolve more zinc, since it attacks the otherwise insoluble zinc femtes. The iron which is also dissolved in this second leach is then precipitated as jarosite, goethite, or hematite. The development of these iron predpitation techniques permitted the use of the hot. strong acid leach and an increase 111 zinc extraction from about 87% to greater Ilian 95%. Simultaneously, the hot acid leach frequently generates a leach residue rich enough in lead and silver to provide significant byproduct value, as well as increased recovery of cadmium and copper. 

Improved raw material utilization via hot acid leaching and iron precipitation as previously described... 

Since the start-up of the zinc plant, the leaching circuit comprised three main steps neutral leaching, hot acid leaching and jarosite precipitation, as shown in the flowsheet of Figure 1. 

Furthennore, it was found that the use of lead-silver residues (residues from the hot acid leach process), which have highly condensed silica, as a seed source is effective. This material can be employed over a wide acid concentration range and, therefore, is plicable to each process of residue treatment. 

Hot (high)-acid leach (HAL) of ferrite. This step is compulsory in almost every ferrite treatment process regardless of the iron precipitation method used. The zinc in the ferrite is brought into solution in an acid leaching step at close to 100 C and an acid concentration above 30 g/L H SO, the so-called hot-acid leach (HAL) ... 

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