Yiran Li

Arsenic removal from aqueous solution using ferrous based red mud sludge

Ferrous based red mud sludge (FRS) which combined the iron-arsenic co-precipitation and the high arsenic adsorption features was developed aimed at low arsenic water treatment in rural areas. Arsenic removal studies shown that FRS in dosage of 0.2 or 0.3g/l can be used effectively to remove arsenic from aqueous solutions when initial As(V) concentration was 0.2 or 0.3mg/l. Meanwhile, turbidity of supernatant in disturbing water was lower than 2 NTU after 24h. The pH range (4.5-8.0) for FRS in effective arsenic removal was applicable in natural circumstance. Phosphate can greatly reduce the arsenic removal efficiency while the presence of carbonate had no significant effect on arsenic removal. Arsenic fractionation experiments showed that amorphous hydrous oxide-bound arsenic was the major components. When aqueous pH was decreased from 8.0 to 4.5, arsenic in FRS was not obviously released. The high arsenic uptake capability, good settlement performance and cost-effective characteristic of FRS make it potentially attractive material for the arsenic removal in rural areas.

Preparation of coagulant from red mud and semi-product of polyaluminum chloride for removal of phosphate from water

Abstract Traditionally, calcium aluminate, caustic soda, lime or aluminum slag was employed as alkali for basicity adjustment in the production of polyaluminum chloride (PACl). In this work, red mud (RM), a highly alkaline waste from alumina industry, was utilized instead of the traditional alkali. A composite coagulant (RMPACl) was prepared from RM and the semi-product of polyaluminum chloride (ACl). Important factors for preparation, such as RM/ACl ratio, reaction temperature and reaction time, were investigated and optimized to be as follows: RM/ACl ratio of 0.25 (w v−1), reaction temperature of 80°C and reaction time of 4 h. The results of coagulation tests showed that RMPACl exhibited better performance than PACl for removal of phosphate. The optimum coagulation pH range of RMPACl was found to be 6.0–8.5. High phosphate removal efficiency (>94.9%) was achieved by dosing RMPACl at the dosage of 147.5 mg l−1. Therefore, RMPACl was considered as a low-cost coagulant, which possessed a good coagulation p...

Evaluation of arsenic immobilization in red mud by CO2 or waste acid acidification combined ferrous (Fe2+) treatment

Arsenic was detected in a red mud (RM) produced during alumina production from bauxite known as the Bayer process. The transporting RM was a mixture of RM solid phase (RMsf) and RM liquid phase (RMlf). The mass content of RMsf in RM is about 30-40%. The alkalinities concentrations in the RMlf were in a range of 37.2 × 10(3)mg/l to 51.5 × 10(3)mg/l. Acidification by CO(2) or waste acid (WA) combined with ferrous (Fe(2+)) treatment was evaluated for arsenic immobilization in the RM. The aqueous arsenic concentration in the RMlf decreased from 6.1mg/l to 0.5mg/l and 0.06 mg/l with the addition of CO(2) and WA, respectively. Ferrous was then added to decrease the aqueous arsenic concentration to be lower than 0.05 mg/l. The cost-effective dosages of CO(2) or WA were 80.1g/l or 26.7 g/l, and the corresponding dosages of ferrous were both 6g/l. A 2(3) full factorial design was employed to evaluate the importance of chemical components of the RM in the cost of arsenic immobilization. High concentrations of arsenic and alkalinities in the RM will increase the cost while the effects of alumina contents varied during the different acidifications. Dissolvable arsenic in the RMsf was 8.2% and 9.5% after the CO(2) and WA combined ferrous treatments, respectively.

Coagulation of arsenic adsorbed ferrihydrite with the use of polyaluminium chloride (PAC) or polyferric sulfate (PFS)

Abstract Ferrihydrite is effective in arsenic removal because of the considerable amount of active hydroxyl groups. Solid–liquid separation of the arsenic adsorbed ferrihydrite from aqueous solution is important for the arsenic treatment technology. Coagulation is a promising process for ferrihydrite separation. Effects of different coagulants on arsenic adsorbed ferrihydrite settlement were investigated. Surface charge significantly decreased after arsenic was adsorbed on ferrihydrite. Turbidity, iron and arsenic removal efficiencies were used to characterize the ferrihydrite settling process. Turbidity removal efficiency with polyferric sulfate (PFS) added was 98.2% when pH was 5.0. Meanwhile, the turbidity removal rate with polyaluminium chloride (PAC) added was 96.3–97.3% when the pH of colloidal suspensions was 7.0–9.0. Arsenic or iron removal rate after 30 min settling was improved from about 40 to 80% with coagulants added. The mean size of flocs after coagulation process was 61.8 μm after PFS was ...