石灰软化法中海藻酸钠强化去除脱硫废水中的SO42-

以实际脱硫废水为原水，在不同石灰乳、聚合硫酸铁、海藻酸钠的复配条件下，对混凝沉淀后溶液SO■浓度、pH值、Zeta电位及矾花粒径、表面形貌、官能团和晶体结构等进行分析，探索石灰软化法中海藻酸钠强化SO■去除机理。结果表明：相比于同时投加7 g/L石灰和40 mg/L聚合硫酸铁，复配海藻酸钠可使出水SO■浓度由3991.15 mg/L降低至3238.60 mg/L(均值),pH值(均值)由9.66升高至9.69。海藻酸钠通过吸附电中和及吸附架桥作用促进胶粒的聚集，在投加量为3 mg/L时形成中值粒径30.41μm的矾花。投加海藻酸钠形成的CaSO₄晶体更加规整，晶簇较为细小但极为密集，强化了SO■去除。红外光谱和X射线衍射分析表明，海藻酸钠的羧基(—COO^-)可能通过螯合Ca²⁺等金属离子促进石灰溶解，从而使CaSO₄结晶效果更好。正交实验结果显示，去除SO■较适宜的复配组合为石灰7 g/L+聚合硫酸铁30 mg/L+海藻酸钠2 mg/L,SO■去除率可达到80.94%。

ENHANCEMENT OF SO42- REMOVAL BY SODIUM ALGINATE IN LIME SOFTENING PROCESS OF DESULFURIZATION WASTEWATER

The mechanism of SO₄2- removal enhanced by sodium alginate in the lime softening method was explored in this study, by treating the actual desulfurization wastewater with different combinations of lime milk, polymeric ferric sulfate and sodium alginate, through analyzing the SO₄2- concentration, pH value, Zeta potential, particle size, surface morphology, functional groups and crystal structure after coagulation. The results showed that compared with the dosing of 7 g/L lime and 40 mg/L polymerized iron sulfate at the same time, compounding with sodium alginate could make the SO₄2- concentration in the effluent decrease from 3991.15 mg/L to 3238.60 mg/L (mean value), and the pH value increase from 9.66 to 9.69 (mean value). Sodium alginate promoted the aggregation of the colloids through the adsorption charge neutralization and adsorption bridging mechanisms, and formed flocs with a median particle size of 30.41 μm at a dosage of 3 mg/L. By adding sodium alginate into the system, the formed CaSO₄ crystals were more regular, and the crystal clusters were relatively smaller but quite dense, thus enhancing the removal of SO₄2-. The infrared spectroscopy and X-ray diffraction analysis indicated that, the carboxyl group (—COO-) of the sodium alginate might facilitate the dissolution of lime by chelating the metal ions such as Ca2+, and the crystallization of CaSO₄ was better. The orthogonal experiment results showed that the suitable compound for SO₄2- removal was composed of 7 g/L of lime, 30 mg/L of polymeric ferric sulfate and 2 mg/L of sodium alginate, and then the removal efficiency was 80.94%.