A kind of method for preparing sodium chromate by acid-dissolved oxidation of chromite

Abstract

The invention discloses a method for preparing sodium chromate from chromite by acid dissolution oxygenation. The method comprises the following steps of adding sulfuric acid into chromite ground into mineral powder, controlling reaction temperature, pressure and time, performing filtration after reaction, adding calcium-containing ores into filtrate to regulate the pH value to 2 to 5.5, performing filtration, adding an alkaline matter into filtrate to regulate the pH value to 4 to 6.5, performing filtration, adding an alkaline matter into filtrate to regulate the pH value to 6.5 to 9.5, and performing filtration to obtain solid chromium hydroxide; beating chromium hydroxide, adding an alkaline matter into beaten fluid to regulate the pH value to 8 to 14, controlling reaction temperature, pressure and time, adding an alkaline matter to regulate the pH value to 9 to 14 after reaction, performing filtration, adding an alkaline matter into filtrate to regulate the pH value to 6 to 9, performing filtration, and concentrating filtrate and crystallizing to obtain sodium chromate. According to the method, an oxidant can be added into chromite for reaction in a pressure strong-acid environment to damage a spinel structure of chromite and increase the dissolution rate of chromite, and the pH value can be regulated to effectively separate chromium ions from impurities.

Description

technical field [0001] The invention belongs to the technical field of mineral processing, and in particular relates to a method for preparing sodium chromate by acid dissolution and oxidation of chromite. Background technique [0002] At present, most of sodium chromate is prepared from chromite as raw material, and several methods are generally used: calcium roasting, calcium-less or calcium-free roasting, ferrochromic alkali solution oxidation, pneumatic fluidized tower continuous liquid-phase oxidation technology, potassium It is a sub-molten salt liquid-phase oxidation method, etc., and sodium chromate is obtained by roasting chromite or high-temperature oxidation with alkali. [0003] The main disadvantage of calcium roasting is that there is a lot of slag discharge, and the slag contains hexavalent chromium as high as 1% to 1.5% (calculated as chromium trioxide), especially containing acid-soluble hexavalent chromium in the form of solid solution, which is difficult t...

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Problems solved by technology

Part of chromium slag is produced as chromium salt, the other part is used as raw material for ferrochrome production, and there is a small amount of untreated chromium slag, which will pollute the environment and increase losses in the long run

[0005] The chromium slag produced by the pneumatic fluidized tower continuous liquid phase oxidation technology and the potassium sub-molten salt liquid phase oxidation method can be used for smelting iron or as an additive for cement production after detoxification at high temperature, but the amount of treatment is limited and the investment is large, which is easy to cause damage. Secondary pollution of the environment

[0006] Currently used acid-dissolving technology for chromite treatment, the main problem is the separation of trivalent chromium and ferric iron

The separation of ferric chromium and ferric iron is commonly done by first reducing ferric iron to ferrous iron, and then adding oxalic acid for separation. In this separation method, oxalic acid is costly and the separation effect is average, and the efficient separation of chromium and iron cannot be achieved. As a result, the content of iron in the prepared chromium product exceeds the standard, so that the chromium product does not meet the requirements

In this method, after the reaction is completed, only iron removal treatment is carried out, and there is no detailed iron removal treatment method, but chromite contains a certain amount of impurities such as magnesium and aluminum. If it is not treated, the purity of the obtained product will decrease. It cannot be improved and affects the quality of the product, so it is necessary to carry out reasonable treatment of these impurities. In addition, the reaction pressure used in this method is low, resulting in poor reaction effect

Dissertation "Research on Clean Production Process of Basic Chromium Sulfate Prepared by Sulfuric Acid Leaching of Chromite, Shi Peiyang, Northeastern University, 2002" discloses the method of treating chromite with sulfuric acid, but the method adopts normal pressure reaction, and its reaction effect is poor. and adopt complex iron removal treatment methods

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