| As a non-renewable resources,nitrate resources is one of the world’s scarce resources.So much attention should be paid to the development of circular economy with the development of China’s nitrate resources,which is contributed to maximize resource conservation and reduce consumption,as important as the comprehensive use of resources,Recycling,improving the efficiency of resource and regeneration rate.The crude salt of sodium nitrate of the experiment contains large amounts of sodium nitrate and a small amount of sodium nitrite.Therefore,the purpose of this experiment is to separate and purify sodium nitrate to prepare industrial grade sodium nitrate,to realize resource reuse and reduce environmental pollution.The content of sodium nitrate is determined by indirect method with the industrial sodium nitrate GB（industrial sodium nitrate GB / T4553-2002）,which is time-consuming and due to the sodium nitrate coarse salt impurities which affects the determination results.In this experiment,the content of sodium nitrate in industrial sodium nitrate mixture was determined by ion chromatography and urea-formaldehyde method,and compared to the national standard method（GB / T4553-2002 industrial sodium nitrate）through the average recovery rate and other indicators.The results showed that the average recovery of sodium nitrate was 100.19% and the average RSD was 0.28%（n = 5）by the national standard method（GB / T4553-2002 industrial sodium nitrate）.The average recovery of sodium nitrate was 100.10% with RSD of 0.37%（n = 5）by ion chromatography.And the urea-formaldehyde method is susceptible to interference of sodium nitrite.The comparison of three methods is also studied for the determination of sodium nitrite in coarse sodium nitrate.The results showed that the average recovery of sodium nitrite was98.28%,the RSD was 1.19%（n = 5）by the national standard method（GB / T4553-2002 industrial sodium nitrate）;the average recoveries of sodium nitrite was 100.18%,the RSD was 0.44%（n = 5）by ion chromatography and 99.83% of sodium nitrite was determined by ultraviolet spectrophotometry.The RSD was 1.94%.The results showed that the ion chromatography method is simple,rapid,accurate and reliable.It can be used for the determination of sodium nitrate and sodium nitrite in crude salt of sodium nitrate in industry.The effect of different filter media on the removal of iron insoluble and other impurities was studied.The results showed that the effect of removing impurities is the best when the crude salt solution A and the crude salt solution B of sodium nitrate are filtered through the silica filter cake.The impurity removal rate of 77.00% and 77.75%,respectively.Because the pores of the filter cake made of silica（below 20nm）arranged uniformly and was smaller than the filter paper and activated carbon powder filter holes,what was more,through the Fan Dehua force,hydrogen bond and the role of covalent bond,which can be filtered more impurities.A filtration removal process provided a good oxidation condition for the subsequent oxidation conversion process and reduced the need for oxidation of the latter period of oxidation.At the same time,the silica filter cake can be used multiple filtration,recycling,reduce costs.In the experiment,sodium nitrite was oxidized by air and hydrogen peroxide respectively and the conversion efficiency of sodium nitrite was compared The results showed that the maximum conversion rate of sodium nitrite was not more than 60% by air,and the conversion rate of sodium nitrite was 96.80% by hydrogen peroxide,also the conversion of Fe2+ reached 89.92%.The optimum conditions for the oxidation of sodium nitrite and Fe2+in the solution of sodium nitrite by H2O2 were as follows: 70.00 g of yellow filtrate A,6.00 g of H2O2（30% mass fraction）,pH=4.5,stirring rate of 300 r / min,water bath reaction at 60 ℃ for 2h.After reaction,the mass ratio of 1: 20 NaOH was adjusted to neutral filtration and drying.The kinetic model of sodium nitrite transformation was established by the relationship with the concentration of sodium nitrite in the process of hydrogen peroxide oxidation.The linear relationship between the concentration of sodium nitrite and ln（cA0 / cA）-t was obtained at different temperatures and the linear relationship was good,indicating that the reaction of sodium nitrite accorded with the first-order reaction model,and Arrhenius specific equation was expressed as k = 8.5668exp（-1870 / T）.The sodium nitrate solution（The concentration of sodium nitrite was 48.66%,the mass fraction of sodium nitrite was 0.13% and the mass fraction of water was 51.22%）after the reaction was concentrated by evaporation and cooled to crystallize.The optimum conditions were as follows: evaporation temperature 110 ℃,cooling and crystallization temperature of 50 ℃,stirring rate of 200rad/s,incubation time of 2.0h.The obtained crystal solution is filtrated with a glass sand crucible and dried to obtain sodium nitrate product,and the purity of the sodium nitrate is up to 99.52% meeting the requirement of the first grade of industrial grade sodium nitrate.Each ton of raw material A through acomplete separation and purification process of its yield of 98.48% of sodium nitrate,estimated profitability of ￥107.91. |
