Method for preparation of sodium chromate by low-nitrogen roasting of chromite and continuous leaching of clinker

Abstract

The invention discloses a method for preparation of sodium chromate by low-nitrogen roasting of chromite and continuous leaching of clinker. The method includes the steps of: (1) selecting chromium ore powder, sodium carbonate and return slag; (2) mixing the selected raw materials uniformly, then feeding the mixture into a rotary furnace, carrying out oxygen-fuel combustion through a total oxygen-fuel system, and controlling the temperature of the materials at 850DEG C-1150DEG C; (3) directly and uniformly injecting pure oxygen gas into the raw material under a material bed in the rotary furnace, and carrying out pure oxygen roasting reaction on the raw material in the rotary furnace; and (4) injecting the roasted clinker into a wet vertical mill, adding a sodium chromate dilute solution or pure water through a metering pump, stirring the substances uniformly, conveying the mixture to a belt filter through a transfer trough, and conducting continuous leaching and filtering to obtain sodium chromate. The method has the characteristics of low energy consumption, high sodium chromate yield, low chromium ore consumption, and low content of nitrogen oxide generated in the flue gas, canachieve continuous production, improves the production efficiency, and can realize clean emission.

Description

technical field [0001] The invention belongs to the technical field of chemical industry, and in particular relates to a method for preparing sodium chromate by low-nitrogen roasting of chromite ore and continuous leaching of clinker. Background technique [0002] At present, chromite and soda ash are reacted at 900-1150°C to prepare sodium chromate, which is usually directly heated and reacted by burning hot flame gas in a rotary kiln. Due to the direct heating of flame gas, the oxygen in the high temperature section of the kiln tail If the content is 8%-12%, it will peroxidize the freshly added raw material and form a molten state, which is easy to form rings or form larger particles, which affects the oxidation efficiency. In the patent CN1109026A, the segmented technology in the furnace is adopted. The injected oxygen content is 70% for roasting, and the oxygen content in the high-temperature section of the kiln tail is controlled below 2%, which can improve the partial ...

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Problems solved by technology

[0002] At present, chromite and soda ash are reacted at 900-1150°C to prepare sodium chromate, which is usually directly heated and reacted by burning hot flame gas in a rotary kiln. Due to the direct heating of flame gas, the oxygen in the high temperature section of the kiln tail If the content is 8%-12%, it will peroxidize the freshly added raw material and form a molten state, which is easy to form rings or form larger particles, which affects the oxidation efficiency. In the patent CN1109026A, the segmented technology in the furnace is adopted. The oxygen content is injected into 70% for roasting, and the oxygen content in the high-temperature section of the kiln tail is controlled below 2%, which can improve the partial oxidation efficiency, but there will still be some rings and sticking phenomena

At the same time, at present, the combustion systems used by all chromium salt enterprises are air-fuel combustion systems, and the nitrogen content brought in through the air is as high as 70%. In the kiln gas at high temperature, nitrogen will be oxidized into nitrogen oxides and discharged into In the atmosphere, it cannot meet the requirements below 200mg / m 3 Emission requirements, in order to reduce the nitrogen oxide content to meet the emission standards, it is necessary to install a denitrification device at the flue mouth or add other reducing substances for treatment. In the patent CN108910950A, the nitrogen oxide gas generated after the reaction is reduced by introducing a reducing agent. However, whether it is to install a denitrification device or add a reducing agent for treatment, it will increase the production cost

After the roasted clinker is generally cooled, it is pulverized with a mill, added with a leaching solution for leaching, and then separated by filtration to prepare a sodium chromate solution. In this method, cooling and milling will consume a large amount of energy, and for Intermittent production, low production efficiency

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