Limestone (CaCO3) is an effective means of neutralizing waste acids. The process involves flowing the waste acids (mixtures of HCl and H2SO4) through a bed of limestone granules. The bed can be 3 ft deep at waste flows of from 1.3 to 2.2 gpm/sq ft of bed area. Recycling the treated effluent (from one to three times) and aeration can also improve performance.
This approach to waste neutralization appears to be financially attractive but has limited reliability. The main reason for decreased reliability is the contamination of limestone by materials such as oil and grease with the subsequent loss of bed activity.
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