Phosphate Removal from Aqueous Solutions using Neutralised Bauxite Refinery Residues (Bauxsol™)

Abstract

Environmental Context.Eutrophication of freshwater and marine ecosystems is a global problem, which is frequently linked to high phosphorus concentrations. The present study investigated the use of Bauxsol™, a modified bauxite refinery residue, to remove dissolved phosphate from water, and has shown that it can be used as a cost-effective adsorbent for treating phosphate-contaminated waters. The results provide water and environmental managers with a new technique for decreasing the phosphate loads in water and wastewater. Environmental benefits include improved water quality, minimisation of excessive plant growth, including potentially toxic blue green algae, and the utilisation of an industrial residue for environmental remediation. Abstract.Phosphate (PO43–) removal by Bauxsol™, a neutralised bauxite refinery residue, was investigated as a function of time, pH, ionic strength, adsorbent dosage, competing ions, and initial phosphate concentration. The results of adsorption and desorption studies indicate that adsorption of PO43– by Bauxsol™ is based on a ligand-exchange mechanism, although the low reversibility pH-independent desorption observed in acid-treated Bauxsol™ indicates a dominance of chemisorption. It was shown that PO43– adsorption onto both Bauxsol™ and acid-treated Bauxsol™ followed a Langmuir isotherm model, with adsorption capacities of 0.21 and 0.48 mmol g−1 at pH 9.0 and 5.2 respectively. Adsorption of PO43– by Bauxsol™ increased with decreasing pH, with maximum adsorption efficiencies obtained at pH 5.2 ± 0.1 (the lowest pH investigated), higher Bauxsol™ to initial phosphate concentration ratios, and increased time. Studies of the effects of competing ions on the adsorption of PO43– by Bauxsol™ indicated that adsorption decreased in the presence of HCO3− ions, whereas SO42–and Cl− ions had little effect, and Ca2+ and Mg2+ ions increased adsorption. These findings suggest that Bauxsol™ could be used as an efficient low-cost adsorbent for treating phosphate-contaminated waters.

Interaction between phosphate and acid-activated neutralized red mud during adsorption process

“…A c c e p t e d M a n u s c r i p t 13 kinetic parameters for pseudo first-order, Elovich and pseudo second-order models are given in Table 2. According to correlation coefficient R 2 , the pseudo second-order model fitted the adsorption process better than Elovich model and pseudo first-order model.…”

“…No study has systemically investigated how the phosphate reacted with AaN-RM. Akhurst et al [13] suggested that Page 6 of 44 A c c e p t e d M a n u s c r i p t 6 chemisorption could be important during phosphate adsorption by AaN-RM. The functional species on AaN-RM surface, which were responsible for the chemisorption, have not been identified.…”

Comparison of several different neutralisations to a bauxite refinery residue: Potential effectiveness environmental ameliorants

“…The neutralisation of the soluble alkalinity for both Basecon™-neutralised and Hybrid materials requires the addition of Ca and Mg in a treatment solution, and the data suggests that the high Ca and Mg loadings of these two materials gives the corresponding increase in P binding. Higher P loadings data have been recorded when UNRM is neutralised using gypsum (Alkaloam™) than for UNRM (Akhurst et al, 2006;Brennan et al, 1994;Despland et al, 2011;Huang et al, 2008;Summers et al, 2000). Hence, a major mechanism for P removal to the solids would appear to be the precipitation of poorly soluble Ca-and Mg-phosphates, and such phosphates, although of low water solubility, remain plant available (Akhurst et al, 2006;Clark et al, 2008;Despland et al, 2011;Huang et al, 2008;Summers et al, 2000).…”

“…These applications are where retention of phosphorous is desired. Table 6 shows that removal rates of P to CNRM, compared to Basecon™-neutralised and Hybrid material, is substantially reduced, hence to control the same quantity of phosphorous requires nearly 4 times the dose rate (Akhurst et al, 2006;Clark et al, 2006;McConchie et al, 1999). Such applications for P removal are in sewage treatments, some soil remediation and in the control of farm effluents and fertiliser applications.…”

“…Moreover, the fine-grained nature of the solids also provides potential surface sorption sites (Akhurst et al, 2006;Clark et al, 2011bClark et al, , 2012Collins et al, 2014;Freire, 2011;Genc-Fuhrman et al, 2005, hence BRR and some neutralised derivatives have been used to treat acid mine drainage (AMD), acidic sediments and soils, and industrial effluents Despland et al, 2011;Munro et al, 2004). In addition, BRR and some neutralised derivatives have successfully been used as a landfill cover, odour reducers, catalysts, road base, fertilizer filler, permeable reactive barriers, as a clay cap, ceramics and glass-ceramic manufacture, geo-polymers, construction materials, and synthetic soils (Barbhuiya et al, 2011a(Barbhuiya et al, , 2011b(Barbhuiya et al, , 2010Despland et al, 2011;Lapointe et al, 2006;Lin et al, 2002;McPharlin et al, 1994;Ordonez et al, 2001;Pan et al, 2003 …”