Optimization of Srp/HAP for  removal of fluoride，iron and manganese from groundwater in mining area by response surface methodology

In order to solve the serious problems of F⁻、Fe²⁺ and Mn²⁺ in underground water of mining area, the serpentine loaded hydroxy-apatite (Srp/HAP) composite adsorbent was prepared by wet chemical coprecipitation method, and the simultaneous removal of fluorine, iron and manganese in underground water was studied. Through batch experiment and CCD response optimization experiment, the effects of dosage, reaction time and pH on the removal efficiency of F⁻、Fe²⁺ and Mn²⁺ were investigated, and a quadratic regression model with the removal rates of F⁻、Fe²⁺ and Mn²⁺ as response values was established. Srp/HAP adsorption and regeneration experiments were carried out to explore its reusability. The results show that the optimal reaction conditions of Srp/HAP treatment of complex water samples with mass concentrations of F⁻、Fe²⁺ and Mn²⁺ of 5 mg/L, 20 mg/L and 5 mg/L respectively are as follows: When 3.64 g/L water sample was added, the reaction time was 120.47 min and the pH value was 6.3, the corresponding removal rates of F⁻、Fe²⁺ and Mn²⁺ were 98.23%, 99.9% and 99.7% respectively. The effluent shall meet the requirements of the 《Standards for drinking water quality》(GB5749—2006).The adsorption process of F⁻、Fe²⁺ and Mn²⁺ by Srp/HAP was well fitted by the CCD optimized experimental model. The absolute error between the predicted value and the experimental value is less than 5%, which proves that the experimental model is reliable. After five times of regeneration, the removal rates of F⁻、Fe²⁺ and Mn²⁺ by Srp/HAP composite particles decreased by 16.13%, 10.5% and 15.4%, respectively, less than 20%. Srp/HAP composite particles can be used as an excellent adsorbent for the treatment of groundwater containing fluoride, iron and manganese ions.