Effect of polyferric chloride (PFC) doses and pH on the fractal characteristics of PFC–HA flocs

Abstract

a b s t r a c tChanges in the fractal characteristics of PFC-HA flocs with polyferric chloride (PFC) doses and coagulation pHs were investigated in this study. A type of PFC coagulant with a hydrolysis degree (B*) of 0.6027 and a Fe(III) concentration of 0.202 mol/L was employed to coagulate HA solutions at five constant coagulation pHs. Zeta potential tests were employed to reveal the coagulation mechanisms. The physical properties of flocs formed in the coagulation process were analyzed by their CCD image morphology, size distribution, and fractal dimensions. Next, microscopic observations and nitrogen-adsorption-desorption methods were conducted to characterize the pore structure and surface fractal dimensions of powders prepared from these flocs through a cryofixation-vacuum-freeze-drying procedure. The PFC doses and coagulation pHs had an obvious effect on the physical characteristics of PFC-HA flocs and their corresponding powders. Generally, in the low PFC dose range, PFC-HA flocs formed under acidic coagulation pHs and charge neutralization mechanisms were larger, had less irregular boundaries or surfaces (lower D 1 value), a more compact structure (lower D 2 value) and more irregular pore surface or pore size distribution in their dried powder than those formed under neutral and alkaline coagulation pHs and physical enmeshment and/or fresh precipitate adsorption mechanisms involved in the coagulation process. After the PFC doses exceeded this range, a gradual reversal phenomenon occurred. Furthermore, there were different specific PFC dosages that were above the critical reversal point for each property of these flocs or powders, such as the median diameter, one-dimensional fractal dimension, two-dimensional fractal dimension, and pore surface fractal dimension. In addition to these characteristics, the most compact PFC-HA flocs were formed at coagulation pH = 6.00 ± 0.05 and a PFC dosage of 4.04 × 10 −4 mol/L (Fe 3+ ), and the loosest flocs were produced at coagulation pH = 7.00 ± 0.05 and a PFC dose of 1.01 × 10 −4 mol/L (Fe 3+ ).

Floc properties of polyaluminum ferric chloride in water treatment: The effect of Al/Fe molar ratio and basicity

“…In the preparation of PAFC, the distribution of Al/Fe species could be controlled by adjusting the Al/Fe molar ratio and basicity (B = [OH À ]/[M 3+ ]), thereby achieving better coagulation performance. The coagulation behavior, floc properties and coagulation mechanism have been well understood for some traditional coagulants, such as PAC and PFC, or some organic-inorganic composite coagulant [8,29,30]. However, few works focused on the properties of PAFC flocs, which has been proved to be more efficient in contaminants removal [27,28].…”

Coagulation performance and membrane fouling of polyferric chloride/epichlorohydrin–dimethylamine in coagulation/ultrafiltration combined process

“…According to the research by Wang et al, sometimes good performance on the dissolved humic acid removal and the suspending flocs removal may not occur concurrently. In addition, Q. Wang et al also found that turbidity removal would reach the peak at pH 6 and change slightly as pH increase, which means that different from HA removal, turbidity can be removed effectively in neutral and alkaline region [3,17].…”

“…Existence of natural organic matter (NOM) in potable water resources is hazardous to human health [1,2], of which humic substances dominate in most of potable water resources [3]. In recent decades, removal of NOM has drawn more and more attention in modern water treatment.…”

Effects of epichlorohydrin–dimethylamine on coagulation and membrane performance of ferric chloride in coagulation–ultrafiltration hybrid process

“…In this way, under acidic condition, charge neutralization between HA molecules (with less negative charges) and FC hydrolysates (more positively charged) would be enhanced. Thus, the demand of FC for would be reduced to achieve the same coagulation effect [30][31][32]. Accordingly, pH 6 was determined to be the optimum pH condition for FC/DAM-ECH coagulation in this study, and its membrane performance in the follow up UF process would also be investigated in comparing with other coagulation methods.…”