摘要：

经传统三联箱处理后的脱硫废水具有高碱度、高硬度和高硫酸根的特点，会使后续处理设备出现结垢、堵塞等问题。针对该难题，采用偏铝酸钠（NaAlO₂）可与废水中的Ca²⁺、SO₄ ^2-反应生成难溶性钙矾石的方法，同步高效去除Ca²⁺、SO₄ ^2-。通过单因素实验考察NaAlO₂投加量〔n（Ca²⁺）∶n（Al³⁺）〕、搅拌速度、反应时间、反应温度等因素对NaAlO₂混凝同步去除脱硫废水中Ca²⁺、SO₄ ^2-效果的影响，进而确定NaAlO₂混凝同步去除Ca²⁺和SO₄ ^2-的最佳反应条件。结果表明：在室温条件下，按照n（Ca²⁺）∶n（Al³⁺）=2∶1向原水（初始溶液pH=11.9）中投加NaAlO₂，以300 r/min搅拌30 min即可将Ca²⁺、SO₄ ^2-有效去除，其去除率分别达到（95.7±0.1）%和（81.1±2.5）%。此外，研究还发现向反应系统中投加0.2 g/L水铝钙石作为晶种，可大幅缩短絮凝体的沉降时间。通过XRD、SEM分析可知，加入晶种后，柱状钙矾石晶体附着在片状晶种上，形成密实的异晶包裹体，从而有效提高了其沉降性能。与传统碳酸钠软化工艺相比，NaAlO₂同步去除脱硫废水中的Ca²⁺和SO₄ ^2-药剂成本降低了25.97%，并且减轻了后续纳滤工艺的处理压力，是一种更为经济高效的处理工艺。

关键词: 脱硫废水, 絮凝, 钙离子, 硫酸根离子, 钙矾石

Abstract:

The wet flue gas desulfurization (FGD) wastewater treated by traditional three-tank process is characterized by high alkalinity, high hardness, and high sulfate, which often leads to severe scaling and clogging in subsequent membrane treatment facilities. To address this challenge, sodium aluminate (NaAlO₂) could react with Ca²⁺ and SO₄ ^2- in FGD wastewater to generate indissoluble ettringite precipitates for their simultaneous efficient removal. The effects of NaAlO₂ dosage〔n(Ca²⁺)∶n(Al³⁺)〕, stirring speed, reaction time and reaction temperature on the simultaneous removal of Ca²⁺ and SO₄ ^2- from FGD wastewater were investigated through single-factor experiments. The optimum reaction conditions for simultaneous removal of Ca²⁺ and SO₄ ^2- by NaAlO₂ were determined. The results showed that Ca²⁺ and SO₄ ^2- could be effectively removed by adding NaAlO₂ to the raw water (initial solution pH=11.9) in the ratio of n(Ca²⁺)∶n(Al³⁺)=2∶1 at room temperature with stirring at 300 r/min for 30 min, and the removal rates of Ca²⁺ and SO₄ ^2- could reach (95.7±0.1)% and (81.1±2.5)%, respectively. Additionally, the study found that adding 0.2 g/L of hydrocalumite as a seed crystal to the system significantly shortened the settling time of flocs. XRD and SEM analyses showed that after the addition of seed crystals, the columnar ettringite crystals were attached to the hydrocalumite seeds to form dense heteroepitaxial encapsulation, which effectively improved its settling performance. Compared to the traditional sodium carbonate softening process, the use of NaAlO₂ for the simultaneous removal of Ca²⁺ and SO₄ ^2- in FGD wastewater reduced the chemical cost by 25.97% and alleviated the treatment burden on subsequent nanofiltration processes. The coagulation process for simultaneous removal of Ca²⁺ and SO₄ ^2- was a more economical and efficient treatment approach.

Key words: desulfurization wastewater, coagulation, calcium ions, sulfate ions, ettringite

中图分类号: 

• X703