A method for producing metallurgical grade alumina from fly ash and recyclable ammonium salt

Abstract

The invention discloses a method for producing metallurgy-grade alumina by taking pulverized fuel ash and recycled ammonium salt as raw materials. The method comprises the following steps: (1) preparing materials; (2) roasting; (3) dissolving; (4) crystallizing; (5) carrying out a liquid-solid ammonolysis reaction; (6) grinding and removing sulfur; and (7) performing low-temperature Bayer aluminum production. The method disclosed by the invention has the advantages that an aluminum salt ammonolysis method suitable for strong acid and weak base is adopted, namely liquid-solid or gas-solid ammonolysis is performed, the production efficiency is improved by over 60 percent compared with that a liquid-liquid ammonolysis method, the process conditions of the ammonolysis method are optimized, optimal process parameters are determined, the obtained product, namely crude aluminum hydroxide, is easy to filter and wash, the model selection of equipment is simple, and industrial mass production can be realized.

Description

[0001] Technical field: [0002] The invention relates to a method for producing metallurgical-grade alumina, in particular to a method for producing metallurgical-grade alumina by using fly ash and recyclable ammonium salt as raw materials. [0003] Background technique: [0004] Fly ash is a waste discharged from coal-fired power plants. With the rapid development of the power industry, the amount of fly ash discharged is increasing day by day. The main substances that make up fly ash are aluminum and silicon. The content of alumina in high-alumina fly ash is more than 30%. In some areas of Shanxi and Inner Mongolia, the content of alumina in fly ash even exceeds 50%. Aluminum oxide and aluminum hydroxide are good sources. [0005] At present, the most important ore resource in alumina production is bauxite. my country's bauxite resources are not rich. According to China Customs statistics, in 2012 China's bauxite dependence on foreign countries was as high as 60%. According...

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Problems solved by technology

The related patent CN 102120596 A discloses a method for preparing aluminum hydroxide by precipitation method. Although the particle size of the obtained aluminum hydroxide is easy to control, the presence of aluminum ammonium sulfate solution requires slow pH value control, alkaline titrant Need to add surfactant, aging time is long, reaction speed is slow, etc.

The related patent CN 101130437 A discloses a method for extracting alumina from low-grade bauxite. The ammonium solution adopts gas-solid reaction, and the amount of ammonium sulfate entrained in the crude aluminum hydroxide product obtained in this reaction form is very large, which not only consumes the entrained The ammonium sulfate also increases the alkali consumption of the next step alkali dissolution process

[0010] At the same time, how to reduce the amount of evaporated water in the process of recovering ammonium sulfate is also a major problem in the process of extracting alumina from fly ash by the ammonium method. When the ammonium solution adopts liquid-liquid or gas-liquid methods, the concentration of aluminum ions in the ammonium aluminum sulfate solution is required to be high. Generally, the aluminum ion concentration is required to be lower than 1mol / L. After the ammonium hydrolysis product is separated from solid and liquid, crude aluminum hydroxide and ammonium sulfate solution with lower concentration are obtained. In terms of alumina, when water is used as clinker dissolution liquid, ammonium solution is in liquid-liquid or gas-liquid form, and the evaporation of water in the ammonium sulfate recovery process is about 35-40t, and the economic benefits are not considerable.

[0011] At present, there is no mature scheme for reference from reaction process control to process condition optimization for liquid-liquid, gas-liquid, liquid-solid and gas-solid ammonolysis methods

In the liquid-solid or gas-solid ammonolysis reaction process, the obtained product aluminum hydroxide is relatively easy to filter and wash. When dilute ammonium sulfate is used in the dissolution link, the concentration of ammonium sulfate entering the ammonium sulfate evaporation link is relatively high, and the entire process system evaporates. The amount of water is greatly reduced, which is about 60% lower than that of liquid-liquid or gas-liquid ammonolysis, but the amount of sulfate radical entrainment in the product is very large, accounting for about 15% of the dry basis weight of crude aluminum hydroxide, and the alkali is consumed in the subsequent process volume increase

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