METHOD OF PRODUCING ARSENIC ACID Russian patent published in 2009 - IPC C01G28/00 

FIELD: chemistry.

SUBSTANCE: sludge from production of non-ferrous metals, containing arsenic, sodium, zinc and cadmium compounds, is dispersed in water with mass ratio solid:liquid = 1:(2.5-3). Small portions of nitric acid are added to the obtained suspension until attaining concentration of HNO₃ from 15 to 20 g/dm³. While stirring, the mixture is heated to temperature ranging from 70 to 90°C and held while stirring for 2 to 3 hours. The residue which contains arsenic compounds and elementary sulphur is filtered from the mother solution which contains sodium, zinc, iron and copper sulphates. The residue is washed and water is added until attaining mass ratio solid:liquid=(1-2):(1-3). Nitric acid is added to the obtained solution until attaining pH = 1.5-2 and hydrogen peroxide is added in stoichiometric quantity of 105 to 110%.

EFFECT: wider raw material base for producing arsenic acid, recycling wastes from production of non-ferrous metals using an environmentally safe method, obtaining two end products - sulphur and arsenic acid.

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