Intensification Extracting Potassium Salt From Low Grade Insoluble Potassium Ore By A Novel Mixed Additive Agents System

Potassium is an alkali metal element and it is rich in the earth’s crust. It exists in a variety of forms which mainly compounds in nature. Potash resources play a key role in the development of the national economy, and it was mainly divided into soluble and insoluble potassium resources. Soluble potash resources are the main sources of producing potash, and they are the most important raw material of producing potassium salts currently. There are five main types of available soluble potash resources so far. But these soluble potash resources reserve less and distribute unevenly. Meanwhile, insoluble potassium resources reserve rich, distribute widely and have a higher quality, especially potassium containing rocks including potash feldspar, alunite, biotite, nepheline, leucite, shale and sand, syenite, volcanic, slate, etc. Therefore, study and develop insoluble potash resources are of great significance. Firstly, utilizing potassium containing rocks can not only relieve the shortage of potassium resources, but also provide a theoretical basis and technology support to achieve sustainable use of potassium resources.Traditional method of calcining potassium containing rocks is roasting under higher temperature, but this method consumes higher energy and pollutes environment. We tried to extract sylvite from insoluble potassium containing rocks by adopting mixed additive agents system. The process is novel and energy consumption is lower relatively, while the extracting rate of potassium is more than 90%. The entire process includes three main steps:(1) Roasting decomposition. Insoluble potassium containing rocks with mixed additive agents was roasted at 800℃and insoluble K+was converted to insoluble K+. (2) Leaching. The roasting slag was leached by pure water at 80℃for 2 h with ratio of liquid to solid 1:1. We could obtain leaching residues and leaching liquids by filtering. (3) Impurity removal and separation of Na+ and K+ in leaching liquids. Firstly, we.removed Ca2+ of leaching liquids, and then tried to separate mixed salt solution by cation exchange resin method and crystallization including alcohol-crystallization and evaporation-crystallization. At last the products were dried to obtain soluble potassium salts.. In this paper, the process of extracting potassium from insoluble potassium containing rocks including potash feldspar and biotite systematically were investigated by adopting mixed additive agents system. The influence of roasting temperature, roasting time, leaching temperature, leaching time, liquid effect of solid ratio and different kinds of additives on the extraction rate of potassium were analyzed. Then, the decomposition mechanism and leaching kinetics were studied in depth by new process. The main contents and results were obtained as follows:(1) The optimized conditions of roasting decomposition process by mixed additive agents were explored and the decomposition mechanism was discussed to identify the reaction rules of the decomposition initially. The optimized conditions of roasting decomposition process were as follows:Roasting 4 h at 800℃ by adopting calcium salts (such as calcium chloride, calcium carbonate, etc.) and sodium salts (such as sodium carbonate, sodium chloride, etc.) mixed additives agents system. The thermodynamic analysis showed that the Ca salt-Na salt mixed additive system could decrease the decomposed temperature of ore effectively and reduce energy consumption.(2) The optimized conditions of leaching process were explored, and kinetics of leaching potassium was discussed to determine the rules of leaching potassium. The optimized conditions of leaching process were as follows:Leaching 2 h at 80℃with ratio of liquid to solid 1:1. Kinetics analysis described that the stage of leaching potassium was mainly controlled by internal diffusion process after fitting by using different kinetic equations.(3) Impurity of leaching lixivium and studied methods of separation from mixed salt solution initially. Adding the appropriate amount of sodium carbonate to leaching lixivium to remove Ca2+. We attempted to separate Na+and K+by cation exchange resin method and crystallization methods including alcohol-crystallization and evaporation-crystallization, respectively. The results showed that cation exchange resin is poor for separating Na+and K+. The XRD patterns of crystallized product showed that, compared with the evaporation-crystallization, the diffraction peaks of KCl is stronger while the diffraction peaks of NaCl is weaker among the products obtained by alcohol-crystallization. Therefore, the separation effect of alcohol-crystallization is better than evaporation-crystallization, but these crystallized methods did not separate Na+and K+completely.