Phosphate adsorption on novel solid sorbents

In recent years, eutrophication at coastal waters and lakes is considered as a serious problem for water pollution. An effective and cheap method is necessary for removal of eutrophying causing substances in particular phosphate. This research investigates removal of phosphate from the contaminated solution by utilization of waste materials such as crab shell, oyster shell and fly ash.; The adsorption studies of oyster shell, crab shell, and fly ash at different phosphorus concentration have been conducted as a function of pH. Oyster shell has its optimum phosphate uptake at 100mg/l, which is about 10mg/g of solid. It has been noted that the highest removal occurs at the pH range of 6 to 6.5 for all influent phosphate concentration. Thermodynamic criteria are used for interpreting phosphate reaction for characterizing the phosphorus status at different pH values by the formation and properties of various forms of calcium. It is observed that at pH below 6 the dominant phase is dicalcium phosphate dihydrate and at higher pH the dominant phase is tricalcium phosphate, where the negative logarithm of total phosphorus ion activity is about 3. At pH of 6 there is equilibrium between these two phases.; Crab shell has highest adsorption capacity in comparison with fly ash and oyster shell. The percent phosphate removal is above 97% for all phosphate influent (5 to 100 mg-P/l) at pH ≥ 8. The pH of solution is an important factor in maximizing the efficiency of crab shell. It is shown at pH below 6 the dominant phase is tricalcium phosphate and at higher pH the dominant phase is dicalcium phosphate dehydrate. At pH of 6 there is equilibrium between these two phases.; Phosphorus removal by fly ash as a function of pH has shown that the highest removal occurs at pH ≅ 9. Three distinctive phases as function of pH is observed. At 5.5 < pH < 7, tricalcium phosphate is the dominant phase, at 7 < pH < 7.5, the dominant phase is dicalcium phosphate dihydrate and at higher pH the dominant phase is varisicite, where the negative logarithm of total phosphorus ion activity is about 2.5.