In this study, the effect of Cr(Ⅵ) in industrial wastewater on the coagulation of different aluminum forms under the influence of different particle concentrations was investigated. The coagulation efficiency was determined by examining the removal rate of turbidity, residual aluminum, and residual chromium and by using the residual pH value, zeta potential, and floc properties of the coagulation to reveal the coagulation mechanism of Cr(Ⅵ) in water under different turbidities. The experimental results show that under low turbidity conditions, Cr(Ⅵ) greatly influences the coagulation process of highly polymerized Alb, yet has no obvious effect on oligomeric Ala. Under high turbidity conditions, particulate matter will adsorb part of the Cr(Ⅵ) in high turbidity water, thus reducing its interaction with Alb. The main role Alb plays in coagulation is charge neutralization. It plays the same role in the stability of the particles and floc regeneration. The main role of Alc formed by hydrolysis of Ala is bridging effects and sweep flocculation, which plays an important role in floc production and strength factor. At the same time, the existence of Cr(Ⅵ) enhances the strength factor of Al13 flocs, but the consumption of some of the positive charge will lead to a reduction in the floc recovery factor.
Keywords: Cr(Ⅵ); aluminum species; coagulation; electric neutralization; fragmentation regeneration.