Continuous, dissolved‐air ion flotation of hexavalent chromium

Abstract

AbstractAn experimental investigation is presented of the ion flotation of dichromate from aqueous solution with a cationic surfactant and using a non‐ionic polymer as a flocculant aid. A dissolved‐air, continuous flow unit is used (with a surfactant‐dichromate premix period of 1 hr.) with a feed rate of 120 liters/hr. of a stream containing from 25 to 100 mg./liter of dichromate. Within the ranges of the variables studied, optimum results are obtained with a molar surfactant to dichromate feed ratio of about 2, a feed polymer dosage of about 3% of the dichromate feed concentration, a recycle rate 200% of the feed rate, and a column detention time of 35 min. With an air requirement of 0.043 liters of air (at STP)/liter of feed delivered at 40 lb./sq. in. gauge, feed streams containing from 25 to 100 mg./liter of dichromate can be readily reduced to 10 mg./liter of dichromate and 30 mg./liter of surfactant. The primary advantage of the process lies in the concentration of dichromate, surfactant, and polymer in a small liquid volume of collapsed foam, less than 1% of the total feed throughput. Foam concentrations are of the order of 10,000 to 20,000 mg./liter of dichromate.