The two most common flocculants—or settling agents—at frac sand mines are polyacrylamide and polydimethyldiallyammonium chloride (polyDADMAC). Although other types of flocculants are in use, these chemicals currently appear to make up a majority of the flocculant use. Both of these compounds are readily biodegradable and monitoring at frac sand mines in the Midwest indicate that there is no evidence of groundwater contamination associated with either of these compounds. Polyacrylamide anionic flocculants are used to enhance settling of solids in the clarifier, or thickener, associated with the process. The clarifier produces an underflow, which is essentially a thick mud. Some facilities use a belt press to convert this mud into a solid or filter cake, which offers easier disposal. It is common for facilities that use a belt press to use a polydimethyldiallyammonium chloride (polyDADMAC) cationic coagulant to enhance the performance of the belt press. This paper provides additional background on each of these chemicals and a detailed analysis of the fate of these compounds using a kinetic model that includes biodegradation and other chemical processes.

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• Barr Engineering

• Flocculant

• Article