Scheelite Slag Turns into Sulphur Fixing Agent

As a solid waste, wolframite residue needs financial and material resources for harmless disposal.

Sulfur containing coal in the coal fired boiler and the sulfur dioxide produced in the combustion process enter the tail gas. Therefore, the tail gas still needs to be treated with desulphurization. If the sulfur content is high, the desulfurization pressure of the tail gas is very large. In addition to sulfur dioxide, coal-fired tail gas also contains a certain concentration of NOX, which is also an environmental pollutant and needs to be removed in flue gas treatment.

Researchers have come up with a good solution. The transformation of scheelite slag into sulfur fixing agent can improve the environment.

According to the content of calcium carbonate and the sulfur content in coal combustion, the mixing ratio between the tungsten slag and coal can be determined according to the relevant chemical reaction equation. The mixture of scheelite slag and coal includes mixing, forklift turning and mixing, driving grab mixing and cement mixer mixing.

Sulfur is burned in the combustion chamber to produce sulfur dioxide. Calcium carbonate and carbon dioxide are generated at high temperature. The sulfur dioxide and calcium oxide produced at high temperature are further oxidized to calcium sulphate. Therefore, sulfur dioxide is fixed to the slag in the form of solid calcium sulfate. Gaseous sulfur dioxide is fixed in solid form such as calcium sulphate and calcium sulfite.

Scheelite slag containing NaOH or Na₂CO₃ can react with sulfur dioxide, and sodium sulfite is further oxidized to sodium sulphate at high temperature; a large amount of carbon dioxide produced by coal can react with NaOH to produce Na₂CO₃, and Na₂CO₃ can improve the effect of calcium carbonate. Calcium carbonate and sulfur dioxide react to form calcium sulfite and further oxidize it to calcium sulfate, that is, calcium carbonate to fix sulfur. Calcium sulfate and sodium sulphate are not corrosive and slag is non corrosive.

As a sulfur fixing agent in the combustion of sulfur containing coal, the scheelite slag is fixed to the slag in the form of calcium sulphate in the form of calcium sulfate (50 ~ 90%), reducing the concentration of sulfur dioxide in the tail gas, reducing the difficulty of the desulfurization of the tail gas and achieving the resource utilization of the waste. 

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