Zinc sulphate is sold in crystalline form and dry zinc sulfate is sold in white powder.
If this substance is contaminated with cadmium, its color will tend to yellow, which is of lower quality and is sold at a lower price.
This substance may be contaminated with the heavy elements lead, cadmium, arsenic and nickel, the main reason being the presence of these elements in the mineral soil zinc.
In this case, as a fertilizer is not suitable for agricultural use and its consumption will cause soil and plant pollution.
Method of production of zinc sulfate
The industrial method of producing zinc sulfate is through the reaction of dilute sulfuric acid
with oxidized zinc mineral soil or slag of zinc smelting furnace and zinc oxides.
However, it should be noted that most zinc slags contain large amounts of chlorine due to the use of ammonium chloride. And the zinc sulfate produced from them will contain a lot of chlorine.
The solution obtained by reacting the soil or zinc concentrate with sulfuric acid contains lead, cadmium, nickel, manganese and cobalt.
Lead sulfate is very low in sediment due to its solubility constant, Ksp, and is separated by a filter press.
To separate cobalt and manganese can be oxidized to ions to higher oxidation states using strong oxidants Such as potassium permanganate
and then increase the pH of the solution using calcium carbonate or hydrated lime, It converted these ions into precipitate and separated them.
This reaction takes place at a high temperature and is called hot purification.
The resulting cake contains cobalt and manganese oxides and is called cobalt cake or hot cake.
Cadmium and nickel, by adding zinc powder to the solution, precipitate as metallic cadmium and nickel due to reduction and replacement with metallic zinc.
This reaction takes place at a low temperature and is called cold refining and the resulting filter cake is called cold cake or nickel cake.
Concentrated zinc sulfate solution is concentrated into polyethylene crystallization pools.
Crystallizer or spray dryer is transferred to obtain sulfate crystals on seven water or sulfate on powder dry.