Method for preparing high-purity calcium fluoride product from acid fluoride-containing wastewater

Abstract

The invention discloses a method for preparing a high-purity calcium fluoride product from acid fluoride-containing wastewater, industrial calcium carbonate and acid fluoride-containing wastewater areused as the raw materials, by controlling the technological parameters of dosage, precipitation time and the like, the calcium fluoride is primarily and secondarily precipitated under the action of air flotation of CO2 produced in the precipitation process, the fluorine resource is efficiently recycled, the high-purity calcium fluoride product is prepared, moreover, the treated water is defluorinated in depth by using a calcium salt, so that the water reaches the emission standard. The flow is simple and convenient and is easy to operate, the operation cost is low, no secondary pollution is caused, the produced calcium fluoride product can replace an acid fluorite powder, and the method has an excellent application prospect.

Description

technical field [0001] The invention relates to the preparation technology of metallic calcium compounds, belongs to the field of waste water treatment and resource recycling, and specifically relates to a method for preparing high-purity calcium fluoride products from acidic fluorine-containing waste water. Background technique [0002] Photovoltaic, chemical, electroplating, electronics and other industries use a large amount of hydrofluoric acid in the production process, and the discharged wastewater often contains high concentrations of fluoride, which is likely to cause water pollution. Fluoride-containing wastewater is often treated by calcium salt precipitation, which is removed by combining calcium ions and fluoride ions to form insoluble calcium fluoride precipitates. This method is low in cost and easy to operate, but a large amount of calcium salt needs to be added in order to discharge fluorine-containing wastewater up to the standard, so a large amount of calci...

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Problems solved by technology

Chinese patent application 201210525940.3 relates to a treatment method for fluorine-containing wastewater in the production of solar cells, including collecting the wastewater in the production process of solar cells as high-fluoric acid water, low-fluoric acid water and alkaline wastewater; Calcium carbonate powder is mixed with low-fluoric acid water to make calcium salt solution, and then reacted with high-fluoric acid water to prepare calcium fluoride solid suspension; part of the obtained calcium fluoride precipitate is washed and dried as calcium fluoride product, and another A part of it is mixed with low-fluoric acid water as the crystallization mother liquor and enters the crystallization fluidized bed. The calcium-fluorine ratio in the fluidized bed is controlled to be 0.5-2:1, the pH is 5-8, and the imported fluorine ion concentration is less than 150mg / L. Calcium fluoride is recovered and seed crystals are continuously replenished to ensure smooth crystallization; this process produces calcium fluoride from fluorine-containing wastewater through reactive crystallization and fluidized bed crystallization. The most important defect is that the process is complicated. Calcium carbonate and low-fluoric acid water are mixed to form a calcium salt solution. During this process, some calcium fluoride precipitates and a large amount of free calcium ions have been formed. After adding a perfluoric acid solution, other impurity ions such as fluorosilicate ions and sulfate ions will be mixed with Fluoride ions form a competitive relationship, thereby affecting product quality and crystallization progress

In addition, the process of recovering calcium fluoride by the fluidized bed crystallization method for low-fluoric acid aqueous solution needs to replenish seeds and collect precipitates in time. The crystallization effect is easily affected by the reaction conditions, and it is difficult to ensure efficient progress at this stage.

[0005] Including the patent documents disclosed above, the traditional coagulation-sedimentation method has many disadvantages in the treatment of fluorine-containing wastewater. For example, when calcium oxide is used as the precipitant, a large amount of heat is released during the treatment process, which has potential safety hazards; when calcium chloride is used as the precipitant , because it does not provide acidity, the precipitation effect on acidic fluorine-containing wastewater is not good, and the treatment cost is high; when calcium hydroxide is used as the precipitant, the calcium fluoride particles generated during the precipitation process are easily wrapped on the surface of calcium hydroxide , which is not conducive to the complete progress of the reaction

In addition, in the existing similar processes, the calcium fluoride content and fluorine recovery rate in the obtained products are relatively low, which makes it difficult to apply on a large scale; some processes are complicated, difficult to operate, high in processing costs, and there are also problems of secondary pollution

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