Polyaluminum Ferric Chloride Research Articles

Synergetic Effect of Organic Flocculant and Montmorillonite Clay on the Removal of Nano-CuO by Coagulation-Flocculation-Sedimentation Process.

The widespread usage of nano-copper oxide particles (nano-CuO) in several industrial products and applications raises concerns about their release into water bodies. Thus, their elimination from drinking water is essential to reduce the risk to human health. This work investigated the removal of nano-CuO from pure water and montmorillonite clay (MC) suspensions using poly aluminum ferric chloride (PAFC) as well as cationic polyacrylamide (PAM) by the coagulation-flocculation-sedimentation (C/F/S) process. Moreover, the PAFC and PAFC/PAM flocculation performance for various nano-CuO particles concentrations, dosages, pH, settling times and stirring speeds were also investigated. The findings showed that the removal of nano-CuO and turbidity in MC suspension were higher as compared to pure water. Moreover, the combined effect of PAFC/PAM on the elimination of nano-CuO and turbidity was also substantially better than the individual use of PAFC or PAM. The efficient removal of CuO was observed in the solution containing higher mass concentration in the order (10 mg/L > 2.5 mg/L > 1 mg/L) with an increased coagulant dose. The improved removal performance of nano-CuO was observed in a pH range of 7–11 under various water matrices. The C/F/S conditions of nano-CuO were further optimized by the Box–Behnken statistical experiment design and response surface methodology. The PAFC/PAM dose resulted in the maximum removal of nano-CuO (10 mg/L) in both pure water (>97%) and MC suspension (>99%). The results of particle monitoring and Fourier transform infrared of composite flocs revealed that the main removal mechanism of nano-CuO may be the combined effect of neutralization, complexation as well as adsorption.

Removal of Tannic Acid Stabilizes CuO Nanoparticles from Aqueous Media by PAFC: Effect of Process Conditions and Water Chemistry.

The increased utilization of CuO nanoparticles (CuO NPs) in various fields has raised concerns about their discharge into water containing a wide range of organic ligands. Moreover, the adsorption of these ligands can stabilize the CuO NPs in drinking water treatment plants. Thus, their removal from potable water is important to mitigate the risk to humans. The present study explored the efficacy of the coagulation–sedimentation (C/S) process for the removal of tannic acid (TA)-stabilized CuO NPs using polyaluminum ferric chloride (PAFC) as a coagulant. Moreover, the influence of process conditions (stirring speed) and water chemistry (i.e., pH and ionic strength (IS)) were also investigated to determine their impact on removal. The results showed that stirring speed in the reaction phase significantly affected the removal due to increased flocculation compared with stirring speed in the mixing phase. In addition, pH and IS affect the colloidal stability and removal efficiency of CuO NPs. A relatively better removal performance (<99%) of CuO NPs was found at lower coagulant dosage in the pH range 6–8. The addition of organic ligands reversed the surface charge potential and enhanced the colloidal stability of CuO NPs, resulting in the destabilization of TA-CuO NPs, thereby reducing the optimum PAFC dosage for removal. By contrast, the IS above the critical coagulation concentration decreased the removal efficiency due to inhibition of the ionic activity of PAFC hydrolysate in the aqueous environment. Fourier transform infrared findings of TA-CuO NPs composite flocs suggest that the primary removal mechanism might be mediated via the combined effect of neutralization, complexation as well as adsorption.

Effects of coagulant morphology and chemical properties on soluble reactive phosphate removal in corn ethanol wastewater

As ethanol production continues to rise around the world, and wastewater discharge requirements for phosphorus become more stringent, it is important that phosphorus removal technologies are evaluated on ethanol wastewater streams. In this study, five coagulating agents with distinct characteristics were evaluated for their soluble reactive phosphate (SRP) removal performance on both a synthetic wastewater sample and a wastewater sample collected from a corn ethanol manufacturer. All coagulants demonstrated a positive correlation between coagulant dose and percent removal of SRP on both samples. Alum and ferric chloride produced the highest SRP removal efficiencies on both the ethanol and synthetic wastewater, indicating that prepolymerized, high-basicity coagulants (e.g., aluminum chlorohydrate, poly-aluminum ferric chloride) are less effective for SRP removal than nonpolymerized coagulants. The background matrix analysis combined with the pH studies revealed that the high alkalinity in the ethanol wastewater has a substantial inhibitory effect on SRP removal capacity that supersedes pH effects. These experimental results suggest that the Al-Al and Al-OH bonds in the heavily hydroxylated and polymerized structure of high-basicity coagulants are very rigid, which could prevent inner-sphere complexation and drive a less effective outer-sphere interaction, thus hindering SRP removal efficiency. PRACTITIONER POINTS: Five different coagulants are evaluated for reactive phosphate removal from wastewater. Alum and ferric chloride show higher removal efficiency than prepolymerized and high-basicity coagulants. Optimal removal pH increases with increasing coagulant basicity.

Application of PAFC/CPAM for the removal of ZnO nanoparticles by enhanced coagulation

To cope with the increasingly severe challenges of zinc oxide nanoparticles (ZnO-NPs) in the field of the aquatic environment, this paper uses poly-aluminum ferric chloride (PAFC) and cationic polyacrylamide (CPAM) as coagulants to enhance the removal of ZnO-NPs from water. In two environments (pure-water environment and kaolin environment) that simulate suspended solids, we studied the dosage, pH, precipitation time, and hydraulic power of ZnO-NPs at three different initial concentrations (1, 2, and 30 mg/L). The effects of various conditions on the performance of PAFC, CPAM, and PAFC/CPAM to remove ZnO-NPs were examined. Results showed that the overall removal rate of ZnO-NPs in the kaolin environment was slightly higher than that in the pure-water environment. In contrast the removal rate of ZnO-NPs in the PAFC/CPAM was significantly higher than that of PAFC or CPAM alone. The coagulation removal conditions of ZnO-NPs were optimized using a response-surface model. Under the best conditions, the removal rate of ZnO-NPs with an initial mass concentration of 30 mg/L in the PAFC/CPAM combination in pure-water and kaolin environments was 98.54% and 99.17%, respectively. Finally, by studying the changes in floc size during coagulation, enhanced coagulation was an efficient method of removing ZnO-NPs from water.

Effect of coagulation on bio-treatment of textile wastewater: Quantitative evaluation and application

To address the challenge of high water consumption, massive wastewater discharge and high pollution risk in textile industries, different countries have chosen various treatment method for textile wastewater according to the location and management of textile enterprises. It is not economical purposely to build separate wastewater treatment plants (WWTPs) for each small-scale enterprise, hence, it is common to treat the wastewater for a group of factories and then complete the treatment via a municipal wastewater treatment plant. However, the complex characteristics of textile wastewater brings some new problems for WWTPs: Textile wastewater contains over 300 mg/L COD, 100 μg/L antimony, 1000 μg/L aniline, some of which are toxic to microbes or non-biodegradable. Coagulation plays an important role in the pretreatment of textile wastewater for removing hydrophobic dyes, decreasing the SS and COD. In this paper, Poly Ferric Sulfate (PFS), Poly Aluminum Chloride (PAC) and Poly Aluminum Ferric Chloride (PAFC) were chosen to improve the biodegradability of the textile wastewater. And then, quantitatively evaluate the biodegradability of wastewater before and after coagulation treatment by analyzing the proportion of different organic pollution, which could be divided into four parts including rapid bio-treated, easy bio-treated, normal bio-treated and non-biological treatment. Results showed that the biodegradability of textile wastewater could be improved by coagulation process, and the contents of organic matter of rapid bio-treated and easy bio-treated could be maximizing when the control condition of coagulation process was optimized. Moreover, because of its characteristics of simple, easy to use, and rapidly online implement, this approach holds a great promise for applications such as investigate wastewater feature deeply, treatment technology optimization, risk control and management.

A new process combination with high water flux and superior treatment performance for stevia sugar liquor

Stevia sugar is widely used in food owing to its advantages of low calorie content and high sweetness. In the production of stevia sugar, stevia leaves are immersed in water to obtain a crude liquor, which contains many impurities, such as proteins, polysaccharides, organic acids, etc. These impurities are removed typically by coagulation and filtration. At present, suppliers of stevia mainly use a “lime + ferrous sulfate (FeSO4)” process as the pretreatment, but residual SO42− can cause hydrogen sulfide corrosion and Ca2+ can affect the safety of subsequent boilers in the process. In this study, polyaluminium ferric chloride (PAFC) was evaluated as a superior coagulant to FeSO4, together with ultrafiltration (UF) and nanofiltration to remove flocs and other organic contaminants. It was found that coagulation by PAFC out-performed FeSO4 and was unaffected by pH, while the performance of FeSO4 was sensitive to pH. At pH 10, FeSO4 had an enhanced coagulation efficiency, but formed soluble Fe2+ complexes with organic substances in the original solution, which adversely affected the quality of the filtrate. Compared with a UF membrane, the NF membrane was more effective in removing contaminants, and more tolerant to membrane fouling. In addition to hydrodynamic flux, measurement of trans-membrane electrical current were used to reflect the severity of membrane fouling. The combination of PAFC as coagulant without pH adjustment, and ultrafiltration, was found to be a simpler and superior treatment for stevia liquor with a high degree of contaminant separation, and avoidance of problems caused by SO42− and Ca2+.

Synthesis and Characterization of Polyaluminum Ferric Chloride (PAFC) Coagulant with Superior Turbidity Removal Capacity from K-feldspar/NaOH Extraction Residues

The aim of this work was to synthesize polyaluminum ferric chloride coagulant with significant coagulation performance employing K-feldspar/NaOH leaching residue as precursor. Potassium extraction from K-feldspar through sodium hydroxide calcination method is carried out at optimum, activation temperature, time, mass ratio of NaOH to K-feldspar ore in a muffle furnace followed by deionized water conventional leaching. The extraction residues are engaged in co-polymerization of aluminum and iron for the synthesis of polyaluminum ferric chloride (PAFC). The favorable conditions, concentration of hydrochloric acid, hydrochloric acid to residue ratio (v/m), temperature, time and pH are comprehensively investigated. Main process conditions for K extraction are: ore particle mass ratio of NaOH/ore 1.5:1, calcination temperature at 500 °C, and calcination duration of 2 hours, which all jointly yielded an extraction of 95% potassium, whereas polyaluminum ferric chloride (PAFC) synthesis favorable conditions are: HCl concentration of 5M, HCl/residue 5.5:1(v/m), time 2 hours, temperature 100 ℃ and pH 7. 99.8% turbidity elimination efficacy from an initial turbidity of 125 NTU kaolin suspension is obtained. The XRD study is implemented for raw ore, slag and leach residue and proved existing all possible structural changes occurred in extraction routes, additionally FTIR and ICP-MS employed in investigation of polyaluminum ferric chloride (PAFC) to reveal the functional group configuration within the elements of a coagulant and component analysis respectively.

Enhanced performance of a novel flocculant containing rich fluorine groups in refractory dyeing wastewater treatment: Removal mechanisms

The cost-effective removals of refractory dyes from wastewater have aroused enthusiasm in environmental protection. Flocculants efficiently separating dyes from water significantly improved the treatment efficiency of biological technology. Herein, a novel flocculant, P(AM-HFBMA) with rich fluorine groups, was prepared via micellar polymerization of hexafluorobutyl methacrylate (HFBMA) and acrylamide (AM) with sodium dodecyl sulfonate (SDS). The relationship between structure and characteristics of P(AM-HFBMA) and performance in dyeing wastewater treatment was investigated. The removal mechanisms of dyes were emphasized in the discussion. P(AM-HFBMA) with rich fluorine groups, amide groups and ester groups performed obviously better than commercial polyacrylamide (PAM) in the treatment. Its rough surface and high surface area conduced to adsorption of dyes by flocculants and flocs. SDS adhered on the surface of P(AM-HFBMA) for the hydrogen bond between them interacted with dyes through charge attraction and hydrophobic association to generated hydrophobic ion-pair. The hydrophobic groups in P(AM-HFBMA) also played essential roles in hydrophobic association with dyes and reinforced the interaction among flocculant, SDS and dyes for their hydrogen bonds. Bridging of P(AM-HFBMA) was found. A cationic inorganic floccualnt, poly aluminum ferric chloride (PAFC), mainly neutralized the negative charges carried by dyes, and its amorphous hydroxyl metal complex strengthened the formation of flocs.

Potential of coagulation to remove particle-associated and free-living antibiotic resistome from wastewater

Coagulation has been accepted as a cost-effective and environmental-friendly method to remove pollutants. In our recent work, two coagulants of polyaluminum chloride (PAC) and polyaluminum ferric chloride (PAFC) with dosage gradients, and one coagulant aid of anionic polyacrylamide (PAM) were used to investigate their potential to remove particle-associated (PA) and free-living (FL) ARGs and MGEs detected by high throughput qPCR (HT-qPCR) method. The results indicated that the maximum removal efficiencies of PA- and FL-ARGs (4.67- and 3.18-logs) were obtained at the PAFC dosage of 50.0 mg/L. Excessive PAFC dosage can hamper the removal of size-fractionated ARGs. As PAC aid, anionic PAM (1.0 mg/L) had limited effects to promote the removal of PA-ARG, while FL-ARG removal was enhanced by 0.34 log at the PAC dosage of 50.0 mg/L. The fitted curves suggested that the optimal chemical dosages of PAC, PAFC and PAC coupled with PAM in the removal of total ARGs and MGEs were 40.5, 64.7 and 50.0 mg/L, respectively. In addition, we found that much more coagulants were needed to remove FL-ARGs compared to that of PA-ARGs. The removal efficiencies of size-fractionated ARGs by flocculation can be affected by coagulant type, dosage, coagulant aid, Zeta potential and microorganism lifestyle (PA or FL).

Synthesis and evaluation of cationic flocculant P(DAC-PAPTAC-AM) for flocculation of coal chemical wastewater

In this study, a high-efficiency cationic flocculant, P(DAC-MAPTAC-AM), was successfully prepared using UV-induced polymerization technology. The monomer Acrylamide (AM): Acryloxyethyl Trimethyl ammonium chloride (DAC): methacrylamido propyl trimethyl ammonium chloride (MAPTAC) ratio, monomer concentration, photoinitiator concentration, urea content, and cationic monomer DAC:MAPTAC ratio, light time, and power of high-pressure mercury lamp were studied. The characteristic groups, characteristic diffraction peaks, and characteristic proton peaks of P(DAC-MAPTAC-AM) were confirmed by fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), 1H nuclear magnetic resonance spectrometer (1H NMR), and scanning electron microscopy (SEM). The effects of dosage, pH value, and velocity gradient (G) value on the removal efficiencies of turbidity, COD, ammonia nitrogen, and total phenol by poly aluminum ferric chloride (PAFC), P(DAC-MAPTAC-AM), and PAFC/P(DAC-MAPTAC-AM) in the flocculation treatment of coal chemical wastewater were investigated. Results showed that the optimal conditions for the flocculation of coal chemical wastewater using P(DAC-MAPTAC-AM) alone are as follows: dosage of 8–12 mg/L, G value of 100–250 s − 1, and pH value of 4–8. The optimal dosage of PAFC is 90–150 mg/L with a pH of 2–12. The optimal dosage for PAFC/P(DAC-MAPTAC-AM) is as follows: PAFC dosage of 90–150 mg/L, P(DAC-MAPTAC-AM) dosage of 8–12 mg/L, and pH range of 2–6. When P(DAC-MAPTAC-AM) was used alone, the optimal removal efficiencies of turbidity, COD, ammonia nitrogen, and total phenol were 81.0%, 35.0%, 75.0%, and 80.3%, respectively. PAFC has good tolerance to wastewater pH and good pH buffering. Thus, the flocculation treatment of coal chemical wastewater using the PAFC/P(DAC-MAPTAC-AM) compound also exhibits excellent resistance and buffering capacity.

Comprehensive reutilization of iron in iron ore tailings: preparation and characterization of magnetic flocculants.

A large number of iron ore tailings (IOTs) are produced in steel industry, posing threat to the environment during its storage and disposal. To effectively reutilize Fe in IOTs, we propose a comprehensive utilization scheme: (1) most Fe in IOTs is extracted by concentrated hydrochloric acid to form FeCl3 flocculants; (2) after separation from the FeCl3 flocculants, a small amount of Fe is absorbed on the residue solids, which is further washed out to synthesize micron Fe3O4 as magnetic seeds. Results show that the as-synthetic FeCl3 flocculants meet the product standard for FeCl3 flocculants in China (GB/T 4482-2018) after a series of treatments including rotary evaporation, neutralization, and dilution and have comparable performance with commercial polyaluminum chloride (PAC) and polyaluminum ferric chloride (PAFC). Moreover, the addition of synthetic superparamagnetic Fe3O4 (as magnetic seeds) doubled the flocculation rate compared with as-synthetic FeCl3 flocculants alone. Finally, the reutilization of Fe in IOTs can create a direct economic value of ¥ 1.27/kg IOTs, and produce 745 g high-silicon residues for further reutilization, which indicates that our comprehensive utilization scheme is of great application potential.

The effectiveness of activated silica derived from rice husk in coagulation process compared with inorganic coagulants for wastewater treatment

Five novels of poly inorganic coagulants were prepared: hydrolyzed poly aluminum chloride (PACl), hydrolyzed poly ferric chloride (PFeCl), poly aluminum hydroxy sulfate (PAHS), hydrolyzed poly aluminum ferric chloride (PAlFeCl) and hydrolyzed poly aluminum ferric chloride plus silicate (PAlFeCl + Si). Each of them was characterized using FTIR, NFTIR and XRD. The samples were compared with the conventional Alum and the commercial PAĆ. Implementations were carried out for the removal of some pollutants from the ground and sewage water. The topmost removal percentages of TSS, COD and BOD in sewage wastewater reached 92%, 88%, and 85%, respectively; using PAlFeCl. Whereas the ultimate removal percentages of Fe+2, Mn+2, TSS, COD and BOD were 99.7%, 99%, 92.0%, 89.0%, 91.0%%, respectively by PAlFeCl + Si. Therefore, PAlFeCl + Si is the superior poly inorganic coagulant, the co-polymer of aluminum and iron coagulants impregnated with silica is considered as a good one for sewage water treatment due to its reasonable price and good efficacy in this application, as well as it will solve the problem of water shortage and it could contribute as non-conventional water resources.

Remediation Technology and Typical Case Analysis of Informal Landfills in Rainy Areas of Southern China

A typical informal landfill in a rainy area of southern China was taken as an example in this study. The comprehensive control ideas and processes of the informal landfill site were systematically reviewed. The basic situation for the early stage of the government survey and investigation was provided, including a waste stock survey, water volume measurement, and a waste source survey. The main contents and key factors of a comprehensive investigation of the environmental quality status were briefly summarized. The water quality in the landfill, groundwater quality inside and outside of the site, and heavy metals in the bottom sediment were all determined. A low-cost practical landfill technology was explored to reduce the Chemical Oxygen Demand CODCr concentration of polyaluminum ferric chloride (PAFC), and NH4+-N was removed by calcium hypochlorite. Soil backfill was replaced, such that the informal landfill site was immobilized, which was perfectly suitable for this southern rainy area. This study proposes rules for a comprehensive improvement scheme for a landfill, and provides a reliable theoretical basis and practical experience for the treatment of similar informal landfills.

Evaluation of four different coagulants used for chemical dephosphorization of membrane bioreactor effluent

A continuous flow chemical reactor was constructed to study the dephosphorization effect on the effluent of the oxygen-limited internal-loop fluidized membrane bioreactor (IF-MBR) for domestic sewage treatment. Removal effect of total phosphorus (TP) by four coagulants of AlCl3, FeCl3, polyaluminum ferric chloride (PAFC) and polyaluminium chloride (PAC) was evaluated. Results showed that when the ratio of coagulants to TP was 5 (coagulants in terms of Fe and Al), the removal efficiency of TP by FeCl3 was 92.5% and the addition of FeCl3 resulted in an increase in the chromaticity of the effluent. PAC and PAFC had good removal of TP, and the removal percentage achieved 96.2 and 97.4, respectively. However, the flocs they produced were small and light, and the performance in settlement was poor. AlCl3 performed well as a phosphorus removal agent, the removal rate of TP reached 97.4%, and the flocs were large and dense. Based on this, AlCl3 was the best choice for IF-MBR and then the experiment further optimized the Al/P ratio. Results showed that when the Al/P ratio was above 1:1, the effluent TP concentration was lower than 1mg/L; when the ratio was higher than 2.5:1, the effluent TP was lower than 0.5mg/L.

Analysis of the Influence of Coagulant on Phosphorus in Landscape Water Environment

This study selected three kinds of inorganic polymer coagulant: polyferric sulfate, polyaluminium chloride, polyaluminium ferric chloride, two inorganic low molecular coagulants: aluminum chloride and aluminum sulfate. The coagulation experiment of lake water without “water bloom” was carried out. The results were analyzed by multivariate linear regression and principal component regression analysis. It showed that the effects of the five coagulants on the phosphorus were the same when the landscape water was treated with different dosages of coagulants. The sequence was: total nitrogen (TN) > dosage > ammonia nitrogen > CODcr > turbidity > PH. Among them: the highest effect of total nitrogen on phosphorus was aluminum chloride (71.73%). The most obvious effect of dosage on phosphorus was polyaluminium chloride (34.68%). The most significant effect of ammonia nitrogen on phosphorus was polyaluminum chloride (16.98%).

A novel process for recovery of aluminum, iron, vanadium, scandium, titanium and silicon from red mud

A novel process for recovery of aluminum, iron, vanadium, scandium, titanium and silicon from red mud was proposed. The parameters of HCl leaching, solvent extraction, polymerization process, alkali leaching with pressure, and aging process were investigated. The results show that more than 96 % of scandium and vanadium could be leached by using HCl with many aluminum, iron and few titanium and silicon from red mud. More than 97 % of vanadium and scandium was extracted by solvent extraction with mono(2-cthylhexyl)2-cthylhexyl phosphonate (P507), but few other elements from the acid leaching solution. The rich vanadium liquid and rich scandium liquid could be obtained by washing the saturated organic phase. More than 97 % of iron and aluminum could be precipitated as the polyaluminum ferric chloride from the raffinate. The rich titanium material of TiO2 with grade of 62 % was obtained by NaOH leaching with pressure from the acid leaching residue. The white carbon black with purity of 99.5 % was obtained by aging with sulfuric acid solution.

Efficient Removal of TiO2 Nanoparticles by Enhanced Flocculation–Coagulation

TiO2 nanoparticles (TiO2-NPs) in water were removed by enhanced coagulation with polyaluminum ferric chloride (PAFC) and cationic polyacrylamide (CPAM). The flocculation efficiency by PAFC and PAFC/CPAM for three different initial concentrations (0.2, 2, and 30 mg/L) of TiO2 nanoparticles in pure water and a kaolin suspension system (kaolin concentration: 30 mg/L) were investigated with different coagulant dosages, pH values, precipitation times, and hydraulic conditions. Results showed that the removal rate of TiO2-NPs in the kaolin suspension system was slightly higher than that in a pure water system, and the removal rate of TiO2-NPs obtained by PAFC/CPAM was significantly higher than that by PAFC alone. The removal efficiency of TiO2-NPs increased with increased initial concentration of TiO2-NPs. Under the optimal conditions, the removal rates obtained by PAFC/CPAM for 30 mg/L initial concentration TiO2-NPs in pure water and the kaolin suspension system were 97.98% and 98.62%, respectively. Studies on...

Effectiveness of synthesized aluminum and iron based inorganic polymer coagulants for pulping wastewater treatment

Three inorganic polymer coagulants, namely, polyaluminum chloride (PAC), polyferric chloride (PFC) and polyaluminum ferric chloride (PAFC) were synthesized and tested for the treatment of simulated pulping wastewater. PAC exhibited the best performance for organics removal from the wastewater among all coagulants. PACs with basicity 2.0–2.7 were synthesized using three basification reagents (Na2CO3, NaOH and CaO) at ambient as well as elevated temperature. The desirable reactive polymeric content (Alb) were found highest in PACs (basicity = 2 and 2.5) using CaO. The synthesized PAC samples were stable for at least a period of 70 days. Among all the coagulants, PAC synthesized with CaO as basification agent (i.e., PAC2o; basicity = 2) showed similar organics removal as that obtained with aluminum salts. Low dissolved Al concentration in wastewater, good settling characteristics (with sufloc), low cake resistance during filtration and significantly improved biodegradability were the major benefits with the synthesized PAC2o.

Treatment of backwater in bauxite flotation plant and optimization by using Box-Behnken design

Abstract Flotation indexes gradually decrease with the increase of cycle time of the backwater in bauxite floatation, and discharge of backwater brings environmental risk. In this study, methods such as Fenton-oxidation, adsorption and coagulation were used in the treatment of backwater, the flotation indexes were checked after backwater treatments, and Box-Behnken design (BBD) was used in the optimization of the main operating parameters. The results reveal that flotation indexes are effectively improved after coagulation treatment by polyaluminum ferric chloride (PAFC). The optimum parameters predicted by BBD are pH 7.55, 1.09 g/L PAFC dosage and temperature of 25 °C. Under these optimum conditions, a maximum recovery of Al2O3 of 82.83% and a minimum A/S of 1.30 of tailings are gained, while the deviations are less than 3% from the predicted values. These findings encourage the application of BBD for the optimization of critical parameters in backwater treatment.

Synergistic coagulation of bauxite residue-based polyaluminum ferric chloride for dyeing wastewater treatment

Considering that Fe, Al elements in bauxite residue are active components for water purification, an effective polyaluminum ferric chloride (PAFC) coagulant derived from bauxite residue, with Fe2O3 content > 5.1%, Al2O3 % > 6.5%, basicity > 65%, was successfully prepared. The effect of as-prepared PAFC on the zeta potential for printing and dyeing wastewater was investigated. Comparing with polyferric chloride (PFC) and polyferric sulfate (PFS) for printing and dyeing wastewater treatment, prepared bauxite residue-based PAFC exhibited the optimal performance in the aspects of chromaticity and chemical oxygen demand (COD) removal rate. Furthermore, the combination of bauxite residue-based PAFC and PFS for synergy coagulation of such wastewater demonstrated an obvious positive effect. With the proportion between as-prepared PAFC and PFS to be 2.5:1, the COD of treated wastewater could be further reduced to meet the national level A standard of China, providing a promising route to solve the problem of substandard printing and dyeing sewage outfall by a simple coagulation strategy.