基于碳酸钙条件溶度积理论的造纸废水好氧曝气除钙

Calcium removal by aerobic aeration of papermaking wastewater based on CaCO_(3) conditional solubility product theory

造纸废水中较高的钙离子浓度会对废水处理带来很大挑战,为实现造纸废水中钙的有效快速去除,首先用条件溶度积理论分析了造纸废水钙离子浓度过高但不能及时有效沉淀的原因,然后结合模拟溶液和好氧原水曝气实验,探讨了造纸废水好氧段曝气除钙的pH变化机理,最后根据曝气过程中条件溶度积的变化情况探索了钙离子沉淀的有利条件。结果表明,好氧原水的碳酸钙条件浓度积Ps最大,最接近理论计算曲线,好氧原水的钙沉淀趋势最明显且最容易沉淀。对好氧原水直接曝气可以促进碳酸钙沉淀,pH呈现出先上升后下降再上升的趋势,这是脱除CO_(2)气体提高溶液碱性与溶液中生成碳酸钙沉淀增加酸性互相竞争的结果。条件溶度积计算表明,pH为7.5~8.5时碳酸钙条件溶度积处于较低值,溶解度最小,该条件有利于钙的沉淀去除。

High concentration of calcium ions is a big challenge for papermaking wastewater treatment. In order to remove calcium efficiently from papermaking wastewater, the problem that the Ca^(2+)concentration in papermaking wastewater is high and Ca^(2+)cannot effectively precipitate was analyzed based on the conditional solubility product theory at first. Through the aeration experiments of simulated Ca^(2+)solution and raw water, the pH change mechanism of the aeration calcium removal from the aerobic section of papermaking wastewater was then discussed. Finally, the favorable conditions for calcium ion precipitation were explored according to the variation of conditional solubility product during aeration. The results showed that the conditional concentration product of CaCO_(3) in aerobic raw water was the highest, and the closest to the theoretical calculation curve,indicating that the calcium precipitation trend of aerobic raw water was the most obvious and the easiest to occur. The direct aeration of aerobic raw water could promote the precipitation of calcium carbonate. The pH values of wastewater increased firstly, then decreased, and increased again. The characteristic pH peak was formed due to the competitive effect of both solution alkalinity rise from the release of CO_(2)and solution acidity rise from the carbonate precipitation during the aeration process. The conditional solubility product calculation of the aeration process showed that the conditional solubility product of calcium carbonate was relatively lower when the pH was at 7.5~8.5, and the solubility of calcium carbonate was the minimum, which was conducive to the removal of calcium precipitation.