Phosphate Recovery from Water Using Cellulose Enhanced Magnesium Carbonate Pellets

摘要

Phosphorus is an essential and limited nutrient that is supplied by a depleting resource, mineral phosphate rock. Eutrophication is occurring in many water bodies which provides an opportunity to recover this nutrient from water. One method of recovery is through adsorption; this study focused on fabricating a porous and granular adsorptive material for the removal and recovery of phosphate. Magnesium carbonate was combined with cellulose in varying weight ratios (0, 5, 10, 15, 20%) to synthesize pellets, which were then calcined to increase internal surface area. Physiochemical properties such as surface area, thermal degradation, surface morphology, elemental composition, and crystal structure of the materials were characterized using Brunauer, Emmett and Teller (BET) surface area analysis, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The pellet proved to be uniform in composition and an increase in BET surface area correlated with an increase in cellulose content until pellet stability was lost. Phosphate adsorption using the pellets was studied via batch kinetics and sorption isotherms. The pseudo-second-order kinetics model fit best suggesting that the adsorption occurring was chemisorption. The isotherm model that fit best was the Langmuir isotherm, which showed that the maximum equilibrium adsorption capacity increased with an increase in cellulose content between 10% and 20%. The average adsorption capacity achieved in the triplicate isotherm study was 96.4 mg g-1 for pellets synthesized with 15% cellulose. Desorption of the phosphate back into solution was studied using solutions that changed pH and only up to 4% was desorbed. Overall, using cellulose and subsequent calcination created additional internal surface area for adsorption of phosphate and suggests that granular materials can be modified for efficient removal from water and need to be studied further for recovery of phosphate post adsorption.