Method of preparing calcium fluoride

Abstract

A method of preparing calcium fluoride comprises the following steps: providing a waste solution containing HF acid; controlling the HF content of the waste solution within a predetermined concentration range; adding a Ca source to the waste solution containing HF acid within a predetermined concentration range; and controlling the reaction temperature of Ca and HF acid within a predetermined temperature range to form CaF2. Accordingly, the method of preparing calcium fluoride of this invention has the advantages of simple process, low costs, high CaF2 preparation speed, and high and stable purity and quality of CaF2 prepared thereby.

Description

technical field [0001] The present invention relates to a method for preparing calcium fluoride, in particular to a method for preparing calcium fluoride by using waste liquid containing HF acid. Background technique [0002] Because hydrofluoric (HF) acid is widely used in the cleaning process of wafers or substrates such as semiconductors, photovoltaic panels, and solar energy, taking Taiwan as an example, the amount of hydrofluoric acid used is extremely high (according to the capacity utilization rate, at least nearly 50,000 to 100,000 metric tons / year), and the discharged waste hydrofluoric acid is at least a multiple of the used amount, because the cleaning process will use ultra-pure water for further cleaning, and naturally more waste liquid containing HF acid will be discharged. The waste liquid containing HF acid must be recycled and treated, otherwise it will cause great pollution and damage to the environment. [0003] Generally, when treating HF-containing acid...

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Problems solved by technology

[0003] Generally, when treating HF-containing acid waste, a large amount of alkali must be consumed for neutralization treatment, and a lot of fine sludge is produced, which is very difficult and expensive to deal with

And, if the fluorine valuables therein cannot be made into industrially usable products such as calcium fluoride (CaF 2 , commonly known as fluorspar), it can only be treated as sludge, which is a waste of resources and uneconomical

[0004] The waste liquids formed by different industries and different processes usually contain different concentrations of HF acid, and the concentration can range from 3wt% to 49wt%. 2 In the method, all did not control the HF acid concentration of recovery waste liquid and did not control reaction temperature, but directly added calcium hydroxide (Ca(OH) 2 ) or calcium chloride (CaCl 2 ) and other calcium sources, so that fluoride ions (F - ) and calcium ions (Ca 2＋ ) produces CaF that is poorly soluble in water (very low solubility product (Ksp)) 2 Precipitate, thus causing CaF 2 The production rate is low, the process time is long, etc.

In addition, since most of the waste liquid contains impurities such as nitric acid or / and sulfuric acid, it will react with calcium to generate calcium nitrate or / and calcium sulfate and react with CaF 2 Co-precipitation, so only CaF with low purity (purity can only reach 50-60%) can be prepared 2

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