有机酸对铝氧化物吸附磷的影响

以存在不同配位阴离子 (硫酸根、磷酸根、草酸根、柠檬酸根 )时合成的铝氧化物为对象 ,用平衡吸附法研究了草酸、柠檬酸等的浓度和 pH对铝氧化物吸附磷的影响 ,并讨论有机酸影响磷吸附的机制。结果表明 :六种合成铝氧化物的最大吸磷量 (Xm)介于 0.189～ 0.838mmol/g ,以Al(OH)x的吸磷量最高 ,铝 柠檬酸复合物 (Al-CA)的吸磷量最低 ;有机酸浓度升高时 ,铝氧化物的吸磷量降低 ,且柠檬酸的影响程度高于草酸 ;先加 pH为 2的草酸或酒石酸 ,Al(OH)x对磷的次级吸附量最低 ,而有机酸pH为 3时 ,Al(OH)x对磷的次级吸附量达最高 ,有机酸溶液 pH由 4增至 9,铝氧化物吸磷量变化不大或逐渐降低。有机酸与磷混合加入同单加磷相比 ,pH 3时差异较小 ,pH 4～ 6时差异最显著 ,pH 7～ 8时又减小 ;有机酸降低铝氧化物吸磷量的机理包括酸性溶解和络合竞争两方面 ,在 pH 2时以前者为主 ,pH 3～ 9时以后者为主 ,且铝氧化物表面的吸附点位对供试配位阴离子都是亲合的

EFFECTS OF ORGANIC ACIDS ON PHOSPHATE ADSORPTION BY SYNTHETIC Al OXIDES

Effects of concentration and pH value of several organic acids on phosphate secondary and competitive adsorption by hydroxides, which were synthesized with AlCl₃ and NaOH in the presence of various anion ligands, were studied by equilibrium adsorption method. The results showed (1) the higher the concentration of organic acids, the more reduction in phosphate adsorption amount was. The reduction degree of P adsorption in the presence of citrate was more significant than that in the presence of oxalate; (2) the amount of P secondary adsorption was the least at pH 2 for organic acid solution, whereas the most at pH 3. From pH 4 to 9, the amount of P secondary adsorption became less. These suggested that phosphate adsorption by different Al hydroxides, secondary adsorption after organic acids adsorbed and competitive adsorption between phosphate and organic ligands were all influenced with kind, concentration and pH value of organic acid solutions. The effect mechanism might include dissolution and ligand effect. At very low pH, dissolution of Al hydroxides was dominant, however, at pH more than 3, ligand competition became the most important.