In the present study, different ratios of layered double hydroxides (LDHs) were synthesized via co-precipitation method. The synthesized LDHs were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), nitrogen adsorption-desorption analysis, point of zero charges (pHpzc), scanning electron microscopy (SEM) and Transmission Electron Microscopy (TEM). Phosphate adsorption performances were estimated by batch adsorption experiments, desorption hysteresis and adsorption mechanism were also investigated. The XRD, SEM and TEM results confirmed the multilayer structure of the synthesized LDHs. The pseudo-second-order kinetic model and the Freundlich model describes the adsorption behavior of LDHs best. The maximum adsorption capacity is 185.86 mg-KH2PO4/g for Mg2Al-NO3 LDH. When the dosage of LDHs is greater than 2 g/L, the phosphorus content in the solution decreased from 30 mg-P/L to 0.077 mg-P/L after adsorption by Mg2Al-NO3 LDH. All the results reveal that Mg2Al-NO3 LDH is a potential adsorbent for removing phosphate from aqueous solution.

An ultrasonic assisted microchannel extraction (UAME) method was developed for the extraction of Fe(III) from wet-process phosphoric acid with di(2-ethylhexyl)phosphoric acid (D2EHPA). The influences of ultrasonic power, extractant concentration, water phase velocity and the ratio of the organic and aqueous phases (O/A) on the extraction rate of Fe(III) were systematically studied. The results showed that the extraction efficiency of Fe(III) reached 91.08%, which was significantly higher than that for ultrasound extraction and microchannel extraction respectively. Response surface methodology was adopted to obtain the optimal conditions and to evaluate the significance of variables affecting the extraction efficiency. The extraction efficiency of Fe(III) reached 92.24% under the following optimum conditions: extractant concentration, 2.1 mol/L; aqueous phase velocity, 0.055 mL/min; ratio of organic phase and aqueous phase, 2.98.

A new extractant PN-1 was synthesized, and an ultrasound-assisted micro-channel extraction (UAME) system was developed for the extraction of magnesium from wet-process phosphoric acid (WPA). The effects of O/A ratio, P 2 O 5 content, initial pH, ultrasound power, and aqueous phase ratio on extraction were investigated. The extraction efficiency of Mg 2+ could reach 89.09% under the conditions of 74 W ultrasound power, 4 O/A ratio, and 0.2 mL/min aqueous phase velocity. The response surface methodology (RSM) result indicated that O/A ratio and aqueous phase velocity have extremely significant influences on extraction efficiency, significant interaction existed between ultrasound power and aqueous phase velocity, and ultrasound power evidently reduced extraction time. Furthermore, the magnesium could be fully stripped by 1 mol/L H 2 SO 4 with a phase ratio lower than 2. Thus, the new extractant PN-1 and ultrasound-assisted microchannel extraction system are suitable for the extraction of magnesium from wet-process phosphoric acid.