The Synergistic Effects of Al3+ and Chitosan on the Solid–Liquid Separation of Coal Wastewater and Their Mechanism of Action

Abstract

It is important to identify an environmentally friendly and efficient flocculant that can replace polyacrylamide for the solid–liquid separation of coal wastewater. In this study, to explore whether chitosan can be used as an environmentally friendly and efficient flocculant for the solid–liquid separation of coal wastewater, AlCl3–chitosan was used to conduct flocculation–sedimentation and dewatering tests under different chitosan dosages and shear-strength conditions for the prepared coal wastewater. Focused beam reflectance was measured to dynamically monitor the number of refractory fine particles, and the settled flocs were photographed and analyzed with microscopy to explore the effect of AlCl3–chitosan on the flocculation settlement effect and floc characteristics. The synergistic mechanisms of AlCl3 and chitosan were investigated using quartz crystal dissipative microbalance and zeta potential measurement. The results showed that the addition of chitosan can significantly improve the flocculation–sedimentation and dewatering effects of coal wastewater. A reasonable dosage under a certain shear strength is conducive to the reduction of fine slime particles, which results in a compact floc structure, increases the floc size, and improves the settling effect. The synergistic effect of AlCl3–chitosan improved the electric neutralization and adsorption bridging abilities of the chitosan, and the mixed solution of AlCl3 and chitosan had stronger adsorption on the carbon surface. This study provides a new approach to the selection of flocculants for coal wastewater treatment.

Preparation of a Lignin-Based Cationic Flocculant and Its Application in Kaolin Suspension Treatment

“…These voids resulted in instability and looseness of the resulting flocculated structure, which increased the resistance of the particles to settle in the liquid. As a result, the settling velocity of the particles decreased [ 24 ]. Simultaneously, loose flocs could lead to a thicker compression layer thickness.…”

“…Different types of flocculants have different effects on supernatant clarity [ 24 ]. Therefore, the dynamic distribution of particles during the flocculation of kaolin suspensions by AL-g-PAMA #5 was investigated using FBRM.…”

“…The dewatering rate was calculated according to Equation (5) [ 24 ] as follows: where is the dewatering rate, cm/min; is the volume of filtrate, mL; is the dewatering time, s; and is the radius of the Brinell funnel, cm.…”

“…where M 0 is the total mass of the beaker and filter paper, g; M 1 is the total mass of the beaker, filter cake, and filter paper after filtration, g; and M 2 is the total mass of the beaker, filter cake, and filter paper after drying, g. The dewatering rate was calculated according to Equation (5) [24] as follows:…”

Preparation of Cationic Polyacrylamide Suspension and Its Application in Oilfield Wastewater Treatment

“…When the dosage of the CPAM suspension was 1.5 times the optimal dosage of the original CPAM particle, the turbidity removal rates were basically the same, with 28.40% and 28.20%, respectively. This is due to the addition of cationic surfactants in the suspension, as cationic surfactants can assist the polyacrylamide adsorption of suspended particles in wastewater through electrostatic action, whereby the more negatively charged suspended particles are in wastewater, the more pronounced is this auxiliary flocculation effect [ 36 ]. As shown in Figure 7 d, for the oilfield wastewater from the Xing-1 combined wastewater treatment station, the wastewater with the addition of the CPAM suspension was obviously clearer and brighter than that with the addition of the original CPAM particles, and the flocs aggregated out of the wastewater were obviously larger.…”