Acidified hydrazine hydrate was used to remediate Cr(VI)-contaminated soil. The content of water-soluble Cr(VI) in contaminated soil was 4977.53 mg/kg. The optimal initial pH of hydrazine hydrate solution, soil to solution ratio and molar ratio of Cr(VI) to hydrazine hydrate for remediation of Cr(VI)-contaminated soil were 5.0, 3:1 and 1:3, respectively. Over 99.50 % of water-soluble Cr(VI) in the contaminated soil was reduced at the optimal condition within 30 min. The remediated soil can keep stable within 4 months. Meanwhile the total phosphorus increased from 0.47 to 4.29 g/kg, indicating that using of acidified hydrazine hydrate is an effective method to remediate Cr(VI)-contaminated soil.

The strong stability of Cu–ethylenediaminetetraacetic acid (Cu–EDTA) results in the low decomplexation efficiency by the traditional Fenton process. For breaking this limitation, a three-dimensional electro-Fenton (3D-EF) system was constructed to study the decomplexation of Cu–EDTA at different pH, and the effects of Fe2+ concentration, particle electrode dosage, current density, and coexisting ions on decomplexation performance were investigated. The results showed that 3D-EF exhibited high pollutant removal efficiency in a wide pH range compared with the traditional electro-Fenton process. The optimal conditions for the removal of Cu–EDTA were as follows: the pH was 7, Fe2+ was 1 mmol L−1, granular activated carbon was 2 g L−1, and current density was 10 mA cm−2, and the optimum Cu–EDTA removal efficiency reached 90.95%. In addition, the presence of Cl− slightly improved the decomplexation efficiency, whereas NO3− and HPO42− inhibited the removal of Cu–EDTA. The kinetics of Cu–EDTA decomplexation in all experimental groups followed the first-order kinetic equation.

Phosphorus widely existing in rainfall and wastewater impacts the water environment. In this study, sludge, cement block, and coal fly ash were employed as ceramsite material to synthesize Al-doped waste ceramsite (Al-ceramsite) for removing phosphate (PO43−-P) from aqueous solutions. Batch static adsorption–desorption experiments were designed to investigate the effect of various parameters such as Al-ceramsite dosage, PO43−-P concentration, temperature, initial pH, coexisting ions, and desorbents on the removal of PO43−-P. Also, the fate of PO43−-P removal efficiency in actual rainwater was studied through dynamic adsorption column experiments using Al-ceramsite. Results showed that Al-ceramsite could remove PO43−-P efficiently under the optimum parameters as follows: Al-ceramsite dosage of 40 g/L, initial PO43−-P concentration of 10 mg/L, temperature of 25 °C, and pH of 5. Besides that, the Al-ceramsite could completely remove PO43−-P in actual rainwater, and the effluent PO43−-P concentration was lower than the environmental quality standards for surface water Class Ⅰ (0.02 mg/L). The adsorption characteristics of Al-ceramsite on PO43−-P by X-ray photoelectron spectroscopy (XPS) were further explained. As a result, ligand exchange and complexation were confirmed as the main PO43−-P removal mechanism of Al-ceramsite. Thus, Al-ceramsite was prepared from industrial waste and has shown excellent potential for phosphorus removal in practical applications.

Ni-ethylenediaminetetraacetic acid (Ni-EDTA) poses serious threats to the ecological environment and human health, due to its acute toxicity and low biodegradability. The decomplexation efficiency of Ni-EDTA through the conventional Fenton process has been constrained to pH; thus, other appropriate approaches are required to destroy the stable chelate structure at a neutral pH. In this study, the effect of operating parameters such as the pH, Fe2+ concentration, particle electrode dosage, current density, and coexisting ions was studied. The results revealed that the 3D-EF system owned advantages for the removal of Ni-EDTA in the broadening of the pH application window. The Ni-EDTA removal efficiency in the 3D-EF system reached 84.89% after 120 min at a pH of 7. In addition, the presence of coexisting ions slightly affected the decomplexation efficiency of Ni-EDTA.