Recovery of phosphate using a zinc oxide/hydroxide and lanthanum hydroxide nanoflower adsorbent prepared via co-precipitation in water

Abstract

Phosphorus is widely used in many industries, but the volume of mined phosphate rock is increasing by 2 % annually, leading to concerns about potential depletion within the next 100 years. Therefore, concern about the recovery and reuse of resources at the risk of exhaustion has increased dramatically. In this study, zinc oxide/hydroxide (ZnO/Zn(OH)2) and lanthanum hydroxide (La(OH)3) nanoflower (ZLNF) with excellent stability and high adsorption efficiency for phosphate were synthesized using low-cost co-precipitation method. The phosphate adsorption efficiency of the ZLNF was 73.2 %, higher than that of pure ZnO/Zn(OH)2 nanoflower (41.0 %) from 0.025 g of adsorbent in 20 mL of initial phosphate concentration of 50 mg/L. The ZLNF was also characterized according to the Zn/La molar ratio, preparation temperature, and pH. The Zn/La molar ratio affected the specific surface area and adsorption performance of the ZLNF, while phosphate adsorption was highly reliant on the pH of the solution, with the maximum adsorption efficiency observed at pH 3. The phosphate adsorption characteristics of the ZLNF were evaluated using isothermal adsorption, kinetic, and thermodynamic models, with the Langmuir and pseudo-second-order models deemed to be the most appropriate. Phosphate adsorption on ZLNF was thus concluded to be a monolayered homogeneous process, with chemical adsorption dominant. In addition, the Langmuir theoretical maximum adsorption capacity was 178.6 mg P/g, much greater than that of other materials reported in previous studies. The results of this study are thus expected to be very useful in the field of resource recovery.