饱和铬酸钠共存苛性碱中铬铁矿的氧化分解行为

Oxidative decomposition behavior of chromite in aqueous sodium hydroxide solution saturated with sodium chromate

为考察铬铁矿苛性碱氧化浸出反应体系循环苛性碱溶液对铬铁矿氧化分解行为的影响,以90℃下饱和铬酸钠共存苛性碱(代替单一苛性碱溶液)作为反应介质,研究了苛性碱浓度、氧气分压、铬铁矿粉粒度、反应温度、反应时间等参数对铬铁矿氧化分解过程的影响规律,分析了铬酸钠与苛性碱的分离效果以及铬酸钠与铝、硅杂质元素的分离效果。研究结果表明,铬铁矿氧化分解的较佳工艺条件为苛性碱浓度50wt%、氧气分压3.2 MPa、铬铁矿粒度小于48μm、反应温度250℃、反应时间240 min。在较优工艺条件下,铬铁矿中铬元素的浸出率达到95.24%;铬铁矿中浸出的铬有96.36%以铬酸钠晶体的形式在后续浸出渣溶解分离过程中进入溶晶液,而铬铁矿中浸出的铝、硅分别有84.92%和95.04%进入到浸出液中;同时,未参与反应的苛性碱有89.41%保留在浸出液中。与苛性碱单一反应介质氧化分解铬铁矿的过程相比,本工作采用的反应方式将从铬铁矿中浸出的主元素铬、杂质元素铝和硅,以及未参与反应的苛性碱分别调整到溶晶液和浸出液中,获得了较好的分离效果。

In order to investigate the effects of recycling NaOH as reaction medium on the oxidative decomposition process of chromite ore, aqueous NaOH solution saturated with NaCrOat 90℃, instead of single aqueous NaOH solution, was chosen as the reaction medium and the effects of alkali concentration,oxygen partial pressure, particle size of chromite ore powder,reaction temperature and reaction time on the chromite decomposition process were systematically investigated. The results showed that, the extraction rate of chromium could reach as high as 95.24% after 240 min at 250℃ with NaOH mass concentration of 50wt%, oxygen pressure of 3.2 MPa and partial size less than 48 μm. As far as the separation efficiency of chromium from alkali and impurities was also considered, about 96.36% of the chromium extracted from the chromite ore was found in the mixed solids of chromite ore processing residue(COPR) and sodium chromate crystal, while 84.92% of aluminum and 95.04% of silicon extracted from chromite ore was found in the leaching liquor of chromite ore under the better process conditions. At the same time, 89.41% of the unreacted NaOH, was found in the leaching liquor of chromite ore. Compared with the original method with single NaOH as the reaction medium, the new reaction mode in this work enabled the main element of chromium from the chromite ore, the impurities of aluminum and silicon from the chromite ore, and the unreacted NaOH to distribute respectively into the leaching liquor of COPR and crystal mixture, and the leaching liquor of chromite ore, therefore achieving a high separation efficiency. It solved the problems of separation of chromium from alkali and impurities in the leaching liquor of chromite ore and leaching liquor of COPR and crystal mixture in the oxidative decomposition process of chromite ore.