SCR Waste Catalyst Reemployment Project

Nitrogen oxide (NOx) is one of the sources of air pollution and poses a great threat to human health. Thermal power plant is one of the main sources of NOx emission. At present, the main dry flue gas denitrification method is selective catalytic reduction (SCR), the key part of which is catalyst.

SCR catalysts generally use TiO2 as the support and rare metal oxides such as WO₃ and V₂O₅ as the active components. Among them, WO₃ content is about 2-10%, V₂O₅ content is more than 0.5%, TiO₂ content is more than 70%, WO₃, V₂O₅ and the total content of TiO₂ is often more than 90%. Generally speaking, the catalyst is valid for three years, the catalyst returned contains a large number of metal elements, improper treatment will cause serious environmental pollution, and titanium metal. Tungsten and vanadium are valuable metals in price quotas and have the necessity of recycling.

At present, the recovery of SCR waste catalyst is carried out in the following ways:

Cleaning, drying, crushing and grinding of SCR waste catalyst to particle size less than 150μm, the SCR waste catalyst powder was mixed with sodium carbonate evenly and sintered at high temperature to obtain sinter. Tungsten and vanadium are leached by adding water to the sintering material through stirring and heating. The leaching solution obtained by solid-liquid separation is sodium salt solution containing tungsten and vanadium, and the leaching slag is titanium-rich material. When the leaching solution is adjusted to pH above 12, the leaching solution is contacted with the organic phase for multi-stage extraction of tungsten. Tungsten enters the organic phase, and vanadium and impurities such as phosphorus, arsenic and silicon are left in the residual liquid after extraction of tungsten. The negative tungsten organic phase and the residual liquid after extraction of tungsten are obtained. After tungsten extraction, the residual liquid was adjusted to pH 9.5-11.5, and the solution was contacted with the organic phase for multi-stage extraction of vanadium.

Through the above process, SCR waste catalyst can separate tungsten, vanadium and titanium from impurity phosphorus, arsenic and silicon, recover and enrich vanadium, titanium and tungsten, put them into the field of environmental protection application again, which not only brings the benefits of resources into play, but also saves the cost of environmental protection.

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