Two methods of removing sulfates from sulfuric acid wastewater through the addition of barium carbonate and the formation of a barium sulfate precipitant were investigated. Optimization of barium carbonate dosage, reaction time and mixing conditions was accomplished for each method prior to evaluating the treatability of the reaction products. A synthetic wastewater consisting of 9 gm/l H2S04 was treated. A soluble sulfate content of 250 mg/l or less remaining after one hour of reaction time was the criterion for the optimization tests.

The first method of sulfate removal consisted of utilizing barium carbonate in directly neutralizing sulfuric acid wastewater. Almost twice the theoretical amount of barium carbonate was required at a paddle mix speed of 250 rpm for completion of the reaction within an hour. The supernatant remaining after settling was highly turbid. This turbidity was easily removed by coagulation using an anionic 150 polyelectrolyte. The sludge was dewatered efficiently by both vacuum filtration and gravity drainage.

Optimum sulfate removal was accomplished by the second method which consisted of adding barium carbonate to the wastewater after neutralization with high calcium hydrated lime. Only the theoretical amount of barium carbonate was required at a paddle mix speed of 500 rpm for completion of the BaCO₃ - CaSO₄ reaction within an hour. The supernatant after settling was acceptable. Experimental values of specific resistance for this sludge were found to be much lower than those values determined for the sludge from the first method. This sludge, however, blinded the sand bed during gravity dewatering.