Study On The Technology For Potassium Enrichment From Bittern Using Zeolite Method And Technology Of Separation Between Sodium Nitrate And Potassium Nitrate

In recent years,the demand for potassium nitrate in the industrial and agricultural markets is increasing.At present,the domestic KNO₃ production process mainly uses NH₄NO₃ and KCl metathesis method.However,the obtained product contains a large amount of ammonium chloride,and has low purity,poor particle size,and high economic benefits cannot be achieved.Therefore,there is an urgent need to develop a low-energy and high-efficiency KNO₃ production method.Based on the zeolite ion exchange technology,this paper proposes a new process for the production of KNO₃,which is potassium enrichment from bittern regarding modified sodium zeolite as the ion exchanger and Na NO₃ as the eluent,and then energy-saving separation between sodium nitrate and potassium nitrate.The process reuses potassium ions in the eluent stages,and reuses the sodium nitrate product as an eluent in the potassium enrichment stage.It has the advantages of high efficiency and low energy consumption,and has application research significance for reducing production cost.Firstly,the potassium enrichment process was studied,including K⁺adsorption and Na NO₃ solution elution.The elution phase was the key process for obtaining KNO₃ brine.Therefore,the effects of eluent concentrations and elution temperatures on the elution process were investigated.The results showed that the effective exchange capacity of the zeolite was24.17 mg K⁺/g,on the condition of 46 wt%sodium nitrate solution and elution temperature of 90°C.Meanwhile,the new technology of superimposed adsorption and recycled elution was studied,compared with the original process,and the elution rate and effective exchange capacity of the zeolite molecular sieve were increased by 7.5%and 2%,respectively.Secondly,according to the phase diagram of.Na⁺,K⁺//NO₃^--H₂O,the process of evaporation concentration and cooling crystallization was adopted to separate sodium and potassium.The effect of different evaporation end temperature and sedimentation temperature on the purity of sodium nitrate was investigated.The evaporation end temperature was 126°C,the thermal insulation sedimentation temperature was 80°C,and the cooling crystallization temperature was 5°C.The purity of the crude sodium nitrate salt was 98.77%,which can be directly used as an eluent to the potassium enrichment process.The mother liquor of potassium nitrate was used to wash the KNO₃ coarse salt to increase the purity to 99%,at a liquid-solid ratio of 1.2:1,at normal temperature.On the basis of this,the scheme of Na NO₃ dissolution and KNO₃ cooling crystallization coupling was proposed.The heat flow simulation was carried out by Aspen plus software,and the temperature convergence was realized.This method effectively utilized the heat exchange between the Na NO₃ dissolution endotherm and the KNO₃ crystallization process exotherm,which reduced the process energy consumption.Finally,focused beam reflection measurement(FBRM)and particle video measurement(PVM)were used to analyze the KNO3 cooling crystallization process in the mixed system online in real time.The matrix transformation was used to realize the conversion between chord length distribution(CLD)and particle size density distribution(PSD),and then according to the particle size balance formula and the moment method,the nucleation and growth kinetics equation of KNO₃ was obtained.The results show that the growth of KNO₃crystal conformed to the law of?L.The effects of stirring rate,cooling rate and endpoint temperature on crystal size,purity and yield were investigated,which provided a theoretical basis for the dynamic control of crystallization.