煤直接液化项目去除高盐废水总硬度的实验研究

Experimental study on removal of total hardness of high salinity wastewater in direct coal liquefaction project

煤直接液化项目废水通过脱酚脱硫脱氨、高效催化氧化、生化处理、反渗透膜浓缩、晶种法蒸发浓缩等工艺处理后产生高盐废水,利用常规双碱法(NaOH+Na2CO3)去除硬度效果较差。实验研究了在废水中分别投加不同体积的氢氧化钠溶液、碳酸钠溶液、磷酸三钠溶液,对沉淀物进行过滤后,取上清液用EDTA法测定总硬和钙硬,验证去除钙镁硬度的效果。结果表明,煤直接液化项目废水中污染物成分复杂,废水中的硫酸钙、COD、钙络合物等对除硬有很大影响,需要使用能够产生溶度积更低的磷酸钙、羟基磷酸钙沉淀物的磷酸三钠溶液替换碳酸钠溶液作为沉淀剂,才能对类似的高盐废水进行除硬。

The wastewater from direct coal liquefaction project was treated by dephenolization, desulphurization and ammonia removal, high-efficient catalytic oxidation, biochemical treatment, reverse osmosis membrane concentration, crystal seed evaporation concentration and so on, the effect of hardness removal by conventional double alkali method(NaOH + NA2CO3)is poor.In this thesis, the wastewater was treated with different volumes of sodium hydroxide solution, sodium carbonate solution and trisodium phosphate solution, the total hardness and calcium hardness of the supernatant were determined by EDTA to verify the effect of removing calcium and magnesium hardness.The results show that the composition of pollutants in the waste water of coal direct liquefaction project is complex, and the calcium sulfate, COD and calcium complex in the waste water have great influence on the hardness removal, to harden similar high-salt wastewater, sodium carbonate needs to be replaced with a trisodium phosphate solution that can produce calcium phosphate and hydroxycalcium phosphate precipitates with lower solubility.