铝酸钙飞灰中钾的回收利用工艺研究

Study on recycling process of potassium from calcium aluminate fly ash

钾是植物营养元素之一,中国是农业大国,同时又是十分缺钾的国家,每年需进口大量钾肥(主要是氯化钾)以满足农业生产的需要。煅烧法生产铝酸钙过程中副产固体废弃物——飞灰,飞灰中包含氯化钾、钾芒硝、钾石膏、硬石膏等矿物,其中氯化钾和钾芒硝属水溶性矿物,水溶性钾质量分数高达23.52%,对其进行回收利用是十分必要的。飞灰的矿物组成表征及相图分析结果表明:采用热溶-蒸发-冷结晶工艺可高效回收飞灰中的钾,联产硫酸钾和氯化钾等含钾产品。该工艺研究结果表明:优选工艺条件为热溶和冷结晶温度分别为90℃和25℃、液固质量比为3.4∶1、溶浸时间为1 h;在此条件下经6次连续浸取可溶解95%左右的钾,蒸发水量控制与理论分析一致,钾的结晶收率可达81.3%。研究表明对于铝酸钙飞灰中的钾可采用溶解-结晶工艺进行回收以生产硫酸钾和氯化钾等产品。

Potassium is one of the plant nutrient elements.China is a large agricultural country,meanwhile,China is deficient in potassium.Every year,a large amount of potassium fertilizer(mainly potassium chloride)are imported to meet the needs of agriculture.A solid waste⁃fly ash is produced in the course of production of calcium aluminate by calcination.The fly ash contains potassium chloride,aphthitalite,syngenite,anhydrite,etc.Among these minerals,potassium chloride and aphthitalite are water⁃soluble.The content of soluble potassium in the fly ash is as high as about 23.52%,so it's necessary to recycle the potassium.The results of its mineral characterization and theoretical analysis based on phase⁃diagram data showed that it was suitable for recycling of potassium to adopt process of thermal dissolution⁃evaporation⁃cold crystallization process.Potassium sulfate and potassium chloride could be produced.The investigation of the process condition and optimization were done.The optimal conditions were as follows:the temperature of thermal dissolution and cold crystallization,the liquid⁃solid ratio,dissolving time were 90℃and 25℃,3.4∶1,1 h,respectively.After continuous dissolving of 6 times,about 95%of potassium was dissolved.According to composition of the leaching liquid,the amount of water evaporation was as same as the theoretical analysis.And 81.3%of potassium was crystallized under the conditions.The results showed that it was available to recycle the potassium from the fly ash by dissolution⁃crystallization process to produce potassium sulfate and potassium chloride.