Zhen Liang

Removal of phosphate from aqueous solution by red mud using a factorial design.

The purpose of the work is to study the adsorption of phosphate on red mud from aqueous solutions using 2(3) full factorial designs. The important parameters, which affect the removal efficiency of phosphate and final pH of solution (pH(f)), such as phosphate concentration, initial pH of solution (pH(i)) and the red mud dosage were investigated. The effects of individual variables and their interaction effects for dependent variables, namely, phosphate removal efficiency and pH(f) were determined. The results of the study showed that phosphate removal efficiency and pH(f) were found to be 97.6% and 10.9 with optimal reaction conditions initial phosphate concentration 25 mg l(-1), red mud dosage 1.5 g l(-1), pH(i) 3.0, respectively. It was found that adequate amount of calcium ions and higher final pH than 9 are ideal conditions for maximum phosphate removal.

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.

Immobilization of Cd, Zn and Pb in sewage sludge using red mud

Sewage sludge is an inevitable end by-product of sewage treatment. Land application provides a cost-effective alternative for sewage sludge disposal. However, sewage sludge contains heavy metals that may limit its application. In this work, red mud was employed for the immobilization of heavy metals in sewage sludge. The effect of red mud amendment on heavy metal immobilization was evaluated using Toxicity Characteristic Leaching Procedure (TCLP) method. The TCLP results showed that the immobilization efficiency of Cd, Zn and Pb was 100, 92, and 82%, respectively, when sewage sludge was mixed with 10% red mud. Tests carried out in leaching columns demonstrated that heavy metal concentrations in the leachate of 10% red mud amended sludge were lower than those of the unamended sludge. Moreover, red mud decreased plant available heavy metal (Cd, Zn and Pb) content from 18.1, 17.2 and 14.6% to 6.9, 11.4 and 7.6%, respectively. Sequential chemical extraction experiments showed that after sludge was amended with 10% red mud, exchangeable fraction was reduced and iron and manganese oxides fraction was increased. Red mud amendment can effectively immobilize Cd, Zn and Pb in sewage sludge before land application.

Mobility of acid-treated carbon nanotubes in water-saturated porous media.

The production, use, and disposal of nanomaterials may inevitably lead to their appearance in water. With the development of new industries around nanomaterials, it seems necessary to be concerned about the transport of nanomaterials in the environment. In this paper, the transport of acid-treated carbon nanotubes (CNTs) in porous media was investigated. Before the mobility investigation, the stability of acid-treated CNT dispersions was studied using ultraviolet-visible spectra and it was indicated that, under the chemical conditions employed in this work, there was no apparent aggregation. The mobility investigation showed that transport of acid-treated CNTs increased with treatment time due to increase in particle zeta potential. Carbon nanotubes treated with nitric acid for 2, 6, and 12 h possessed measured zeta potentials of -30.0, -43.0, and -48.5 mV, respectively. Utilizing clean-bed filtration theory, we showed that acid-treated CNTs have the potential to migrate 3.28, 5.67, and 7.69 m in saturated glass beads, respectively. We showed that solution ionic strength and pH have important effects on the mobility of acid-treated CNTs. Increasing the pH from 6.0 to 7.9 resulted in an increase in migration potential from 2.96 to 10.86 m. Increasing the ionic strength from 0.005 to 0.020 M resulted in a decrease in CNT migration potential from 5.67 to 1.42 m.