Study On The Decomposition Liquid Characteristics And Dynamics In Carnallite Cold-Decomposition Process

The crystallizer process control of KC1production by carnallite cold-decomposition method is the key of product size and purity. In order to achieve the high quality KC1production, it is necessary to monitor the Mg2+concentration in decomposition, then carnallite feed, water added and volume flux of KC1slurry will be controlled accordingly.Carnallite decomposition liquid characteristics were studied in cold-decomposition and batch-crystallization process. The effect of decomposition temperature and MgCl2concentration in decomposition liquid on decomposition rate of low sodium carnallite were obvious, the higher decomposition temperature was, the faster decomposition rate was, and the higher MgCl2concentration in decomposition liquid was, the slower decomposition rate was. MgCl2concentration in decomposition liquid were17wt.%and19wt.%respectively, when the decomposition temperature was25℃, the complete decomposition time of carnallite was1minute and2minutes respectively; when the decomposition temperature was-10℃, the complete decomposition time were3minutes and4minutes respectively.In the low sodium carnallite decomposition process, the equation of decomposition liquid density and MgCl2concentration in decomposition liquid was linear, and the equation of decomposition liquid salinity and MgCl2concentration in decomposition liquid was linear too, both the slope of linear equations decreased with increasing decomposition temperature. And the slope decreased with increasing MgCl2concentration in decomposion liquid. For example,17wt.%MgCl2in decomposition liquid was used to decompose carnallite, when the decomposition temperature was-10℃, the relationship of decomposition liquid salinity(y) with MgCl2concentration(x) in decomposition liquid was: y=15.104x+50.778, at25℃, it was:y=9.2055x+152.25. When the decomposition temperature was-10℃,19wt.%MgCl2in decomposition liquid was used, the relationship between decomposition liquid salinity(y) and MgCl2concentration(x) in decomposition liquid was:y=11.362x+129.31.The effects of decomposition temperature on the current and the voltage of carnallite decomposition liquid were obvious, and linear equations were obtained. When the voltage was constant, the higher decomposition temperature was the better electrical conductivity of decomposition liquid was observed. With2V initial voltage, the relationship between decomposition current(y) and decomposition temperature(x) was:y=0.0069x+0.5582; and equation of decomposition voltage(y) and decomposition temperature(x) was:y=-0.0135x+1.8414. The higher crystal slurry density was, the better electrical conductivity of decomposition liquid was. The relationship between the decreases of decomposition liquid current(y)(under the same voltage experimental condition, the changes of decomposition liquid current in the state of crystal slurry with decomposition liquid current in the state of clarification) and crystal slurry density(x) was:y=0.6461x-0.0323. The effect of decomposition liquid concentration on the electrical signals was small. So during the carnallite cold-decomposition and cold-crystallization process, decomposition temperature and crystal slurry density changed continuously, decomposition liquid electrical signals changed little.Low sodium carnallite dissolution process was controlled by both diffusion and surface reaction processes, but it was controlled by surface reaction with mixing. At different decomposition temperature, MgCl2concentration decomposition liquid were17wt.%and19wt.%respectively, Stumm equation of Mg2+concentration in decomposition liquid vs. time were as follows:-10℃, dc/dt=4.0092(5.6533-c)1.8916, dc/dt=3.5601(5.9068-c)2.7239;0℃, dc/dt=4.4769(5.7058-c)1.8031, dc/dt=3.8981(5.9091-c)2.4282;10℃, dc/dt=5.7452(5.7261-c)1.7388, dc/dt=3.7778(6.0233-c)2.2603;25℃, dc/dt=5.7429(5.7429-c)1.5862, dc/dt=4.0554(6.0488-c)2.0845.In low sodium carnallite cold-decomposition process, both KCl nucleation rate(Bo) and KCl growth rate(G) increased with increasing KCl crystal seed size. The equations were as follows: B0=8.906×1013exp(-2.44×104/RT)△C1.8762L1.4347; G=5.192×10-5exp(-2.376×104/RT)△C0.7622.