The natural discoloring power of filter aids can be greatly increased by an acid treatment which generates the so-called “activated earth”. The acid treatment of diatomaceous earth eliminates alkalis and calcium, reducing the contents of magnesium, iron and aluminum in it. The acid treatment can be carried out by using either sulfuric acid (H2SO4) or hydrochloric acid (HCL). Calcium oxide is used for the neutralization of the spent acid.
The production process of filter aids from diatomaceous earth essentially involves the following operations. The crude material is mixed with water to form a suspension to which sulfuric acid is added. The mixture is then heated by steam in a mixing tank up to a temperature of 40oc and kept at this temperature for about 4 hours. Then the mixture is heated to 180oc for one hour. After cooling the suspension is filtered through a filter press and washed in order to eliminate excess acidity. The cake of the activated earth is then dried through a pneumatic conveyor by hot air (700oc). The product is collected in a depot and then packed. The activated earth is packed in craft paper bags of 50kg. Filling operations are carried out manually. Any leak of sulfuric acid that could be generated will be washed by water and neautralized to a PH of 6-8 so that it will be disposable with out harming the environment.