Natural Volcanic Tephra for Phosphate Removal from Rural Micro-polluted Wastewater

Abstract

A kind of volcanic tephra (VT) as abundant natural mineral in China was studied for phosphate (P) removal from rural micro-polluted wastewater. Physical and chemical properties of VT were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD), UV-visible diffuse reflectance spectrometry, and Fourier transform infrared spectroscopy (FT-IR). The uptake of P decreased with the increase of the initial solution pH, and the optimum solution pH required for maximum P removal rate was 2.0. Zeta potential analyses were carried out to vividly describe the surface charges at different solution pH. The equilibrium data were both fitted well for Langmuir and Freundlich isotherm models. Thermodynamic parameters including changes in standard enthalpy (ΔH 0 ), standard entropy (ΔS 0 ), and standard Gibbs free energy (ΔG 0 ) were calculated. The removal of P was predominantly based on ionexchange process when the initial solution pH in the range of 2.0-6.0. A given dose of VT can be recycled for eight times. VT minerals were attempted for P removal from rural micro-polluted wastewater collected in Shanghai, China containing 50 mg L −1 P, and the removal rate was determined to be nearly 100 % with the capacity of 0.5 mg P/g VT minerals. All our results indicated that VT could be a promising choice for P removal from micro-polluted wastewater in rural area with the distinct advantages of being low cost and environmentally benign.