Solubility Determination Of Potassium Salt And Formulation Design Of Liquid Fertilizer

Liquid fertilizer is a late-model fertilizer with high efficiency and quick effect,which is applied through irrigation system.Formulating liquid fertilizer is supposed to satisfy the proportioning requirement of abundant chemical elements N,P,K,which is constrained by solubility.Crystallization and sedimentation often occur in liquid fertilizer when it is under the condition of low temperature and they will not only affect fertilizer’s utilization efficiency but also block up transporting apparatus and spray drippers.In this paper,the liquid-solid equilibria of five potassium salts(KCl,KNO3,KH2PO4,K2HPO4,K2SO4)in water are studied at room temperature and low temperature in order to provide basic data for formula design of liquid fertilizer.The main research contents are as follows:(1)The liquid equilibria data of KCl-KH2PO4-H2O,KCl-KNO3-H2O,KCl-K2SO4-H2O,KNO3-KH2PO4-H2O,KNO3-K2HPO4-H2O and K2SO4-KH2PO4-H2O are determined by isothermal dissolution equilibrium method under the temperature of 278.2 K,288.2 K and 298.2 K.This paper also determines equilibrium solid phase composition by wet slag method and the ternary equilibrium phase diagram is drawn and divided into unsaturated zone,single salt crystallization zone and co-crystallization zone.And the results show that all the six systems are simple co-saturated and there are no double salt and solid solution to form.With the increase of temperature,the solubility of KCl,KNO3,KH2PO4,K2HPO4 and K2SO4 in water increases and the area of unsaturated zone is enlarged.(2)The salt solution equilibrium equation and Pitzer model equation of mixed electrolyte are combined to obtain the multiple linear equations about Pitzer parameters.The Pitzer single salt parameters of KCl and K2SO4 at different temperatures are calculated by empirical equation.The Pitzer single salt parameters and Pitzer mixed ion interaction parameters of KH2PO4,KNO3 and K2HPO4 at different temperatures are fitted according to the solubility experimental data.By using the calculated parameters of single salt and mixed ion,the nonlinear equation of salt solution equilibrium constant with respect to ion concentration is solved by MATLAB software,and the theoretical solubility of six experimental systems is obtained.The calculated results are in good agreement with the experimental values.(3)Taking two ternary equilibrium phase diagrams KCl-KH2PO4-H2O and KNO3-KH2PO4-H2O as examples,the formulation area of liquid fertilizer in line with NY 1106-2010 standard is drawn.Based on the liquid-solid equilibrium data,the formula of high potassium liquid fertilizer with N-P2O5-K2O ratio of 7.06-3.14-9.80 and high phosphorus liquid fertilizer with N-P2O5-K2O ratio of 5.4-9.6-5.0 and 6.0-9.6-5.0 are designed with water and biogas slurry concentrate as solvent respectively,and the solubility of the formula is investigated.