【作者】 王飞；

【导师】 胡国荣； 彭忠东；

【作者基本信息】 中南大学 ， 电化学工程， 2009， 硕士

【摘要】 三氧化二铬广泛应用于国防、电工合金、硬质合金、真空电镀、颜料、耗材、高纯合金等方面。目前三氧化二铬通常采用重铬酸钠与硫酸铵热分解法和铬酸酐热分解法制备,生产过程中均需采用剧毒的六价铬化合物为原料。本论文研究了可以用于生产三氧化二铬的绿色无污染新工艺。以高碳铬铁合金粉为原料,成功制备了三氧化二铬。获得的主要结论如下:研究表明120ml浓硫酸浸出100g高碳铬铁合金粉,酸欠量浸出,其实验终点pH值为1.0左右,浸出率达到75%左右;而滤渣中的未反应的铬铁合金粉可与下批铬铁合金粉混合浸出,这样既可以充分利用硫酸,同时也可以节约后面调节pH值时碳酸钠的用量。本文研究了两种浸出液除铁方法:针铁矿法和草酸法。针铁矿法考察了溶液中铬离子浓度、温度、pH值对除铁率及铬损失率的影响。结果表明,针铁矿法除铁的最佳条件为反应温度94℃,溶液pH=2.5,溶液中铬质量浓度为7.0g/L,搅拌强度200r/min,在此条件下,铁的去除率高达99%,铬的损失率为15%;草酸除铁的最佳实验条件为:pH值2.5,草酸为理论值的150%,反应温度30℃,在此条件下,铁的去除率可达99%,且Cr³⁺损失微量。通过实验进行对比研究针铁矿法与草酸除铁法,针铁矿法成本较低,但是在除铁过程中会有15%的铬损失并进入除铁渣中;而草酸除铁法,成本虽高,但是铬铁分离效果良好,不会造成铬的损失,且生成的草酸亚铁是制备磷酸铁锂正极材料的主要原材料。针铁矿法考察了溶液中铬离子浓度、温度、pH值对除铁率及铬损失率的影响。草酸除铁后溶液中还会含有其它金属杂质离子,通过研究加入二硫代氨基甲酸钠可将其除去。最佳除杂实验条件为:二硫代氨基甲酸钠加入量为杂质离子和的理论值,pH控制在2.5左右,搅拌强度为200r/min。以实验中得到的草酸亚铁为原料制备LiFePO₄/C正极材料,LiFePO₄/C材料充放电平台较好,1C放电容量为140mAh·g^-1,粒度分布均匀,可以作为制备磷酸铁锂正极材料的原材料。针对氢氧化铬难以过滤、洗涤,不利于工业化生产的问题。本文研究了溶液中Cr³⁺浓度、温度、pH值以及添加剂聚丙烯酰胺（PAM）对Cr³⁺的沉淀回收率及Cr（OH）₃沉淀过滤性的影响。实验结果表明,溶液中铬离子回收的最佳实验条件为反应温度≥85℃,溶液中Cr³⁺浓度≤10g/L,溶液pH值7.0,搅拌强度200r/min,在此条件下,铬的回收率可达99%,并且Cr（OH）₃沉淀具有较好的过滤性,有利于工业化生产。最后采用热重-差热法研究了Cr（OH）₃的分解过程,并成功地制备了三氧化二铬。研究发现Cr（OH）₃的分解分为三步:首先在50～150℃温度范围内脱掉水分子;其次在200～500℃度范围Cr（OH）₃进一步分解,在400～500℃完成最终脱水形成Cr₂O₃,在此温度范围内样品失重率为26.63%,与Cr（OH）₃分解时的理论失重26.21%几乎相同。因此本实验采取了500℃的保温温度并制备了三氧化二铬样品,此样品满足冶金级三氧化二铬产品标准。更多还原

【Abstract】 Cr₂O₃ is widely used in national defence, electrical alloys, hard alloys, vacuum galvanization, attrited materials, paint, et al. At present, chromium oxide is commonly produced by thermolysis of sodium bichromate, ammonium sulfate and chromic anhydride, and there is serious pollution of Cr⁶⁺ in the production. In this paper, pollution-free technology method of the preparation chromium oxide was studied. Chromium oxide was successfully produced from high-carbon ferrochrome alloy powder. The main results were as follows.The study showed that 100g high-carbon ferrochrome leached by 120ml sulfuric acid which was not enough, The extraction rate of high-carbon ferrochrome reached above 75%, and the final pH value of the leaching was about 1.0. The residue of unreacted high-carbon ferrochrome was reacted with the next high-carbon ferrochrome, which is full utilization of resource and save the quantity of sodium carbonate in the next experiment procedure of pH adjusting. Two removing iron methods was studied in the paper, Iron （III） removed by goethite and iron （II） removed by oxalate. The effects of Cr³⁺ concentration, pH, and temperature on the removal of iron were examined in the goethite process. The results showed that when Cr³⁺ concentration was 7.0g/L, temperature was 94℃and pH=2.5, rate of agitation was 200 r/min, more than 99% of iron is precipitated and 15% of chromium was lost; The optimal experimental condition of iron removed by oxalate was that pH=2.5, oxalate was 150% of theoretical value, reaction temperature was 30℃, more than 99% of iron was precipitated and loss ratio of chromium was little. The experiment studied and compared goethite process to iron removed by oxalate. The cost of goethite process is lower, but 15% chromium entered residue; By contrast, although oxalate method had more cost compared to goethite process has better separation effect. The process not only did not lost chromium but also produced ferrous oxalate which is main material used as the precusor in synthesizing lithium iron phosphate （LiFePO₄）. After iron removed by oxalate, other metal ions in the chromium sulfate solution was removed by sodium dithiocarbamate. The results showed that pH=2.5, rate of agitation was 200 r/min, sodium dithiocarbamate was the theoretical value. The results showed that LiFePO₄/C with uniform particle distribution and good charge-discharge curves and displayed 140 mAh·g^-1 at 1C rate. The ferrous oxalate can be used as the precusor of preparing lithium iron phosphate. Cr（OH）₃ is difficult to filter and wash, which is unfavorable for the industrialized production. The effects of Cr³⁺ concentration pH temperature and polyacrylamide（PAM） additives on the filtering property of Cr（OH）₃ and recovery rate of Chromium were studied. The results of experiment showed that under the optimal conditions of Cr³⁺ concentration below 10 g/L, temperature more than 85℃, pH 7.0 and agitation rate 200 r/min, the recovery rate of Chromium reached 99%, and the filtering capability of Chromium hydroxide was also improved, which was beneficial to industrial production.Finally, the decomposed process of Cr（OH）₃ compound was studied by TG/DSC method and Cr₂O₃ was successfully obtained. The results showed Cr（OH）₃ compund decomposed with three periods. Decomposition of water is between 50¹50℃,and decompose of Cr（OH）₃ is between 200～500℃. The formation process of chromium oxide is between 400～500℃in which Cr（OH）₃ lost the ratio of 26.63%. It is almost the same with the theoretical value which lost the ratio of 26.21%. Cr₂O₃ was prepared at holding temperature of 500℃, and the samples was satisfied standards of metallurgical chromium oxide.更多还原