Selective flocculation performance of amphiphilic quaternary ammonium salt in kaolin and bentonite suspensions

Abstract

In the present work, a type of amphiphilic alkyl quaternary ammonium salt, dimethyl distearylammonium chloride (DAC), was introduced and used as a selective flocculant in kaolin and bentonite suspensions. The selective flocculation property was evaluated by turbidity tests, floc size measurements, zeta potential variation, contact angle measurements and scanning electron microscopy (SEM) observation. The results indicated that an appropriate amount of DAC could achieve selective flocculation at alkaline condition. Based on the experimental facts from size, zeta potential and contact angle measurements, the different flocculation mechanisms of kaolin and bentonite were also investigated. For kaolin suspension, charge neutralization was quite predominant. At different pH level, a low dosage (45 mg/L) of DAC always caused excellent flocculation while high dosage (> 45 mg/L) gradually leaded to restabilization owing to the electrostatic exclusion. For bentonite suspension, bridging effect played the key role. Under acidic condition, bentonite particle always performed good flocculation phenomena at different DAC dosages. But it would gradually lead to enhanced flocculation efficiency from poor to good with increasing the dosage of DAC under alkaline condition. As a result, DAC showed the selective flocculation performance by controlling the dosage of DAC and pH, which provided us the guidance on designing more effective selective flocculant in complex clay mixture system.