Method for extracting aluminum oxide from fly ash

Abstract

The invention discloses a method for extracting aluminum oxide from fly ash. The method comprises the following steps of: a, acid-method treatment: mixing hydrochloric acid and fly ash, and transferring the mixture in a digester, of which the lining is made of polytetrafluoroethylene materials, for digestion, performing the separation of the pulp digested in a settling tank, evaporating and crystallizing upper-part overflow, baking the crystals to decompose the crystals into active coarse aluminum oxide and hydrogen chloride gas, wherein the hydrogen chloride gas is recovered to make acid and the acid is returned to the fly ash settling step; and b, bayer method treatment: mixing the active coarse aluminum oxide and circulating mother liquor, transferring the mixture in the digester for digestion, separating the pulp digested by settlement, performing refined filtration of the upper-part overflow to obtain refined solution, mixing the refined solution and aluminum hydroxide crystal seeds, decomposing the crystal seeds to obtain decomposed mother liquor and aluminum hydroxide, and filtering, washing and baking the aluminum hydroxide to obtain the aluminum oxide product, wherein the decomposed mother liquor is evaporated and then returned to the step of digesting the active coarse aluminum oxide. By adopting the method of the invention, the metallurgical-grade aluminum oxide meeting the requirements on national standards 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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