Study On Treatment Of Wastewater Containing Phosphate By Synthesizing LDH In Situ

Based on the synthesizing principle of layer double hydroxide (LDH), a new method was proposed to remove phosphate and pyrophosphate ions by synthesizing LDH in situ. The objective of this work was to investigate the efficiency and impacting factors of removing phosphate and pyrophosphate ions from wastewater by synthesizing LDH. The principle of the method may be described as follow: Mg²⁺ and Al³⁺ hydrolysize and form Mg/Al-LDH by adding Mg²⁺, Al³⁺ and NaOH into the wastewater containing phosphate and pyrophosphate ions, and the phosphate and pyrophosphate ions are selectively intercalated into the interlayers of LDH to balance the positive structural charges while Mg²⁺ and Al³⁺ co-precipitate and form LDH. The phosphate and pyrophosphate ions in wastewater are removed in the form of LDH precipitate, which was confirmed by analysis of the X-ray diffraction spectra, FT-IR spectra, TEM images and the carbonate exchanged into the precipitate as well as the chemical analysis of the aqueous solutions. The results indicate that the impacting factors on the removal efficiency of phosphate and pyrophosphate ions are amount of Mg²⁺ and Al³⁺ added, Mg/Al ratio, pH and temperature of wastewater. The maximal removal efficiency of phosphate and pyrophosphate ions can be attained when the pH values are between 7.0 and 10.0, and Mg/Al ratios between 1:1 and 4:1; meanwhile, the Mg and Al added can be taken good use of. The water quality of the effluent conforms to the standards for industrial wastewater discharge, and it turns out to be better to apply this technique than the chemical precipitation by using Al³⁺ salts alone. Compared with the anionic exchange of LDH, this method leaves out the industrial process of LDH synthesis, and the two separate processes can be carried out in only one system at the same time.