Study On The Preparation Of Nitrogen Magnesium Compound Fertilizer And Magnesium Salt Whisker From Bloedite Processing

Bloedite(Na₂SO₄·MgSO_4·4H₂O)is stored largely in China.The rational development and comprehensive utilization of bloedite are rarely got.The processing of bloedite by urea salting out and the magnesium salt whisker prepared by hydrothermal method are studied.The solubilities of the quaternary system Na₂SO₄-MgSO₄-CO?NH₂?₂-H₂O and its two subsystems MgSO₄-CO?NH₂?₂-H₂O,Na₂SO₄-CO?NH₂?₂-H₂O were determined by isothermal method at 0?,and corresponding phase diagrams were generated and analyzed.By analyzing and calculating the phase diagram of Na₂SO₄-MgSO₄-CO?NH₂?₂-H₂O at 0?,a technology was designed to separate bloedite.In addition,solubilities of the quaternary system CO?NH₂?₂-MgSO₄-?NH₄?₂SO₄-H₂O at 0?and 25?were studied by isothermal method.ThecorrespondingsubsystemsMgSO₄-?NH₄?₂SO₄-H₂Oand?NH₄?₂SO₄-CO?NH₂?₂-H₂O were determined by isothermal method at 0?.Under the experimental data,phase diagrams were constructed.Based on the characteristic of the phase diagrams,a new technology to separate?NH₄?₂SO₄ and CO?NH₂?₂ from urea waste water is proposed by using the sulfuric acid neutralization and concentrated crystallization.Based on the phase diagrams analyzing and calculating,MgSO₄·?NH₄?₂SO₄·6H₂O and CO?NH₂?₂ can be obtained using MgSO₄·CO?NH₂?₂·2H₂O and?NH₄?₂SO₄ as raw materials.However,MgSO₄·CO?NH₂?₂·2H₂O compound fertilizer and?NH₄?₂SO₄ can not be obtained by using MgSO₄·?NH₄?₂SO₄·6H₂O and CO?NH₂?₂ as raw materials.Magnesium carbonate whisker and magnesium carbonate hydroxide were prepared via reaction between MgSO₄ and Na₂CO₃.The effect of concentration of magnesium sulfate,raw material ratio,reaction time and temperature,and other factors on the conversion of magnesium sulfate and the morphology of the product were investigated.The corresponding products were analyzed and characterized by X-ray?XRD?diffraction analysis and scanning electron microscopy?SEM?in this work.The results indicated that the optimum conditions to synthesize magnesium carbonate whisker with well crystallization are under 50?for 40 min with 1.2mol/L magnesium sulfate and raw material ratio 1:1.2.Under this condition,conversion of magnesium ions can reach 82.35%.The optimum conditions for preparing the basic magnesium carbonate were determined.The results show that:when the reaction temperature is 50?,mole ratio of reactants 1:1.1and the pyrogenation temperature 85?,raw material MgSO₄ concentration is 0.3mol/L,the products of basic magnesium carbonate is mostly rod-shaped of rosette-Like morphology.At the same time,the preparation technology of magnesium carbonate whisker and basic magnesium carbonate by bloedite as raw materials were designed respectively and the recycling of the mother liquor was realized.Using the hydrothermal reaction and static hydrothermal method with MgSO4·7H2O and NaOH as raw material,the preparation of 153 type magnesium sulfate whisker?153MOS?and 152 type magnesium sulfate whisker?152MOS?was studied respectively.The experiment explored the influence of different concentration of reactants,reactant ratios,reaction time and reaction temperatures for the preparation of 153MOS and152MOS.The corresponding products were analyzed and characterized by X-ray?XRD?diffraction analysis and scanning electron microscopy?SEM?in this work.And then the best preparation conditions for preparing the 153MOS were obtained,which are c?MgSO₄?=1.6mol/L,t=4hours,n?NaOH?:n?MgSO₄·7H₂O?=1.5:1,T=180?.The technology of sodium sulfate separated after cooling liquid of 153MOS,and the 153MOS prepared through the hydrothermal reaction again by adding MgSO₄·7H₂O and NaOH to thesolutionaftersodiumsulfateseparationwasdesigned.The optimum conditions for preparingthe 152MOSweredetermined,whichare n?NaOH?:n?MgSO₄·7H₂O?=1.5:1,c?NaOH?=0.8333mol/L,T=150?,and t=33 hours.The base magnesium sulfate whiskers showed that it had a fan shape,the length of the product was 100 microns and the diameter of the product was 1.0 microns.By analyzing and calculating the phase diagrams of Na₂SO₄-MgSO₄-H₂O at 0?,a technology was designed to produce magnesium sulfate hydroxide whisker and by-product sodium sulfafe decahydrate using bloedite as raw material.