Method for extracting alumina from fly ash

Abstract

The invention discloses a method for extracting alumina from fly ash. The method comprises the following steps of: a), acid treatment, i.e. mixing and feeding hydrochloric acid and the fly ash into a digester lined with a polyfluortetraethylene material for dissolving, carrying out separation on dissolved slurry by a settling tank, carrying out evaporation, crystallization, roasting and decomposition on the upper overflow slurry to form active initial alumina and hydrogen chloride gas, and returning the hydrogen chloride gas to a fly ash dissolving process after the hydrogen chloride gas is recovered to prepare acid; and b), Bayer process treatment, i.e. mixing the active initial alumina and circulating mother liquor, sending the mixture into an autoclave for dissolving, carrying out separation on the dissolved slurry by the settling tank, carrying out fine filtering on the upper overflow slurry to obtain refined fluid, mixing the refined fluid and seed crystals of aluminium hydroxide, carrying out seed crystal digestion to obtain decomposition mother liquor and aluminium hydroxide, returning the decomposition mother liquor to the process of dissolving the active initial alumina after the decomposition mother liquor is evaporated, and carrying out filtering, washing and roasting on the aluminium hydroxide to obtain an alumina product. Due to the adoption of the method, the metallurgical alumina which meets the national standard requirements can be prepared.

Description

technical field [0001] The invention relates to a method for extracting alumina from fly ash, more specifically, to a method for extracting metallurgical grade alumina by treating high-alumina fly ash with hydrochloric acid-Bayer method. Background technique [0002] At present, about 70 million tons of alumina are produced every year in the world, and almost all alumina plants use bauxite as raw material. my country is the world's largest producer of alumina, producing about 21 million tons of alumina in 2008, accounting for about 30% of the world's total output. However, my country's bauxite resources are relatively poor, and the bauxite reserves only account for about 6% of the world's total reserves. The ore grade is low, and the ore type is mainly difficult to handle. , and the production cost is also higher. Due to the shortage of bauxite resources in my country, my country imported about 25 million tons of bauxite ore in 2008, accounting for about 50% of the domestic...

AI Technical Summary

Problems solved by technology

The disadvantage is that it is difficult to remove iron and impurities, the quality of alumina products is different from the traditional national standards, and some technological problems still need to be studied and tested

[0008] Patent application CN 1927716A discloses a method for extracting alumina in fly ash, which has the advantage of combining the advantages of acid and alkali methods for preparing alumina, but due to the limitation of process equipment, this method has the following problems: using The "negative pressure concentration in the concentration tank" process is economically unreasonable, so the evaporation process cannot be used industrially, and can only be used for laboratory research; the dissolved slurry is separated and washed in the settling tank to obtain the liquid content of the leaching residue As high as 70-80wt%, it is directly sent to the waste residue dump, which has a great impact on the surrounding environment; the acid dissolution temperature is 90-110°C, and it is found through experiments that the hydrochloric acid dissolution rate of alumina at this temperature is only about 60%, and the dissolution rate is too low It increases the production cost of alumina

Therefore, it is necessary to develop a reliable process method to improve the dissolution effect of alumina in fly ash and solve the problem of corrosion of equipment by hydrochloric acid medium at high temperature

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