Pyrolusite filters

Effluent concentrations of iron and manganese from a pyrolusite filter can be as low as 0.05 ppm. 

The crude manganese dithionate solution is heated to boiling and small portions of powdered barium hydroxide are added until a sample of the mixture, when filtered and acidified slightly with hydrochloric aeldf gives no more test for sulfate ion with dilute barium chloride solution, (Sulfate is formed as a by-product in the oxidation of the sulfur dioxide by pyrolusite. Low temperatures of reaction minimise the formation of it). An excess of barium hydroxide does no harm as it is removed later. 

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