煤化工高盐废水复分解法制备硫酸钾实验研究

Experimental research of preparation of potassium sulfate from high-salt wastewater in coal chemical industry by double decomposition method

煤化工厂生产甲醇和轻烃过程会产生大量废液,将废液经过反渗透和纳滤膜浓缩以及减量处理可以得到高盐废水。以高盐废水为原料,将其浓缩至对硫酸钠饱和,然后采用两步转化法(复分解法)制备硫酸钾:第一步,向浓缩废水中加入氯化钾制备钾芒硝,产生的母液蒸发一部分水分得到氯化钠,向蒸发后的母液中加入硫酸钠得到浓缩母液,回收利用母液;第二步,以钾芒硝为原料加入氯化钾制备硫酸钾。考察了高盐废水浓缩倍率、氯化钾加入量、蒸发水量对钾芒硝纯度及产率的影响;考察了加水量、氯化钾加入量对硫酸钾纯度及产率的影响。得出以高盐废水为原料制备硫酸钾的适宜条件:制备钾芒硝过程,高盐废水浓缩倍率为4.35,以500g浓缩废水为基准,氯化钾加入量为84.25g,蒸发水量为100g;制备硫酸钾过程,以100g氯化钾为基准,钾芒硝用量为153.08g,加水量为322.06g。在此条件下得到的硫酸钾中水溶性氧化钾的质量分数为52.96%、氯离子质量分数为1.09%,符合GB/T20406—2017《农业用硫酸钾》优等品的要求。制备钾芒硝过程,母液循环利用3次,总有机碳(TOC)对钾芒硝的纯度影响不大,对白度有影响;钾芒硝与氯化钾制备硫酸钾产生的母液K,经过投加硫酸钠制备钾芒硝得到母液K″,母液K″与浓缩废水制备钾芒硝产生的母液F组成基本一致,验证了循环工艺路线的可行性。

The process of methanol and light hydrocarbon production in coal chemical plant produces a large amount of waste-water and the high salt wastewater can be obtained by reverse osmosis,nanofiltration membrane concentration and reduction treatment.Potassium sulfate was prepared from high salt wastewater by two-step conversion(double decomposition) after being concentrated to saturate sodium sulfate.In the first step,aphthitalite was prepared by adding potassium chloride to concent- rated wastewater.Sodium chloride was obtained by evaporating part of water from the mother liquor and the mother liquor was concentrated by adding sodium sulfate,also the mother liquor was recycled.In the second step,potassium sulfate was prepared from aphthitalite by adding potassium chloride.The effects of concentration ratio,potassium chloride dosage and amount of evaporation water on the purity and yield of aphthitalite were investigated and the influence of the dosage of potassium chloride and water on the purity and yield of potassium sulphate were determined.The optimum conditions for the preparation of potassium sulfate from high-salt wastewater were concluded as follows:In the process of preparing aphthitalite,the concentration ratio of high salt wastewater was 4.35 times,the addition of potassium chloride was 84.25 g,and the amount of water evaporation was 100 g based on 500 g concentrated wastewater.In the process of preparing potassium sulfate,the dosage of aphthitalite and water were 153.08 g and 322.06 g based on 100 g potassium chloride,respectively.The mass frac- tion of K2O and Cl- in potassium sulphate were 52.96% and 1.09%,respectively,which was in line with the requirements of premium grade in the standard of agricultural potassium sulfate(GB/T 20406-2017).After the mother liquor was recycled for 3 times in the preparation process of aphthitalite,TOC has little effect on the purity and has an effect on the whiteness of aphthitalite.The mother liquor K was produced by the preparation of potassium sulfate by aphthitalite and potassium chloride,and the mother liquor K″ was obtained by adding sodium sulfate to the mother liquor K.The composition of mother liquor K″ was basically consistent with that of mother liquor F produced by concentrated waste water to prepare aphthitalite,which verified the feasibility of the circulating process route.