Removal Of Phosphate From Wastewater By Bittern-Heat Treated Red Mud

Red mud (RM), a kind of bauxite processing waste, can cause serious environmental problems due to its high alkalinity and large amount. RM, however, is a porous material consisting mainly of ferrum, aluminum, tectosilicate-like compounds etc. and is a good candidate for use as an economic adsorbent for large-scale use. An excessive presence of phosphate in wastewater is one of the main causes of eutrophication that affects many natural water bodies. Eutrophication can disturb the balance of organisms present in the water and affect water quality. This study investigated the removal of phosphate from wastewater by bittern-heat treated red mud.Heat treatment was examined in the experiment of red mud modification. The results showed that under the condition of RM to bittern ratio was1:14g·mL-1, roasting temperature450℃for2.5h, the modified red mud (RM-BH) achieved the highest phosophate removal percentage (about96.33%).In the batch experiments, various factors such as dosage of RM-BH, initial pH, contact time, phosphate concentration, temperature and coexist anions were taken into account, and promising results were obtained. The experiments demonstrated that initial phosphate concentration awfully effected phosphate adsorption. The maximum loading adsorption amount was12.89mg·g-1at100 mg·L-1of phosphate concentration. Phosphate removal efficiency was found to be98.81%under optimal reaction conditions with initial phosphate concentration50mg·L-1, RM-BH dosage5.6g·L-1, respectively. The influence of coexist anions such as NO3-, SO42-, Cl-and CO32-on the phosphate adsorption was tested. And the result showed that CO32-promoted phosphate adsorption and the others of them had little influence. The applicability of the Langmuir adsorption isotherms was well than the Freundlich adsorption isotherms for the adsorption. Compared of many kinetic models, kinetic data were fitted with pseudo-second-order model. The thermodynamic analysis indicated that the adsorption was spontaneous and endothermic.RM-BH also showed high efficiency for the removal of both orthophosphate and total phosphate from the livestock wastewater. The percentage removal of orthophosphate and total phosphate were94.71%and86.38%, respectively with the dosage of RM-BH9.6g·L-1at room temperature. Simultaneously,32.51%NH4+-N was removed from the wastewater.