Process method for producing aluminum hydroxide by seed decomposition of supersaturated sodium aluminate solution

Abstract

The invention discloses a process method for producing aluminum hydroxide by seed decomposition of supersaturated sodium aluminate solution. Local stirring is carried out at the bottom of a seed decomposition tank with the stirring strength being capable of keeping aluminium hydroxide particles at the bottom of the seed decomposition tank at a suspension state, so that sodium aluminate solution with high solid content and high molecular ratio, at the bottom of the seed decomposition tank, can be diffused and subjected to mass transfer, and the aluminium hydroxide particles at the bottom of the seed decomposition tank can not deposit. The process method disclosed by the invention breaks through a conventional process line requiring full-mixed-flow stirring in the seed decomposition process, provides a new process method including local stirring and plug flow, and has the characteristics of good energy-saving and consumption-reducing effects, high decomposing output rate, good product quality and the like.

Description

technical field [0001] The invention relates to a process for producing alumina, in particular to a process for producing aluminum hydroxide by decomposing supersaturated sodium aluminate solution seed crystals, and belongs to the field of metallurgy technology. Background technique [0002] The production of alumina by Bayer method has the characteristics of simple process, convenient operation and high product quality. At present, more than 90% of the alumina produced in the world is produced by the Bayer process. In the process of producing alumina by the Bayer process, adding seeds to supersaturated sodium aluminate solution for decomposition reaction is one of the important processes, usually called "seed decomposition process", referred to as "seed separation process". Add a large amount of aluminum hydroxide as a seed crystal to the sodium aluminate solution to induce crystallization and growth of aluminum hydroxide crystals, decompose the supersaturated sodium alumi...

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Problems solved by technology

The seed separation tank adopting the air full-mixing method has simple structure, low manufacturing cost and low maintenance cost. However, this method also has some shortcomings: a) Large power consumption

Although this kind of strong stirring can prevent the crystals from depositing and accumulating at the bottom of the decomposition tank, the shear force generated in the flow field of the sodium aluminate solution will destroy the crystal growth process of aluminum hydroxide on the one hand, resulting in the crystallized and grown hydrogen Alumina particles are crushed, eroded, and refined, which reduces product quality and is not conducive to the output of sandy alumina products

In addition, due to the large volume of the decomposition tank, the mechanical stirring device is tens of meters long, and the stirring load is relatively large, not only the manufacturing requirements for the stirring shaft, stirring blades and other components of the stirring system are relatively high, but also the energy consumption is relatively large. Expensive manufacturing and installation costs, high operation and maintenance costs

A seed tank with a diameter of 14 meters and a height of 35 meters needs to be equipped with a 75-kilowatt stirring motor and gearbox, which is relatively expensive; and the motor runs continuously without stopping production or stopping, which consumes a lot of power

Years of production practice has proved that whether it is air full mixing or mechanical full mixing, it will cause the upper and lower liquids to mix with each other (commonly known as "short circuit"), reducing the supersaturation of the sodium aluminate solution delivered to the seed tank. degree, the reaction efficiency is reduced; at the same time, the strong full mixed flow agitation also causes the particle size of the product to decrease

In 1985, the French Piccini Aluminum Company invented the "method and equipment for producing alumina by decomposing sodium aluminate solution without stirring" (CN85108251A or US4666687). phenomenon, but the invention is only applicable to cylindrical-conical small-scale seeding tanks (1500M 3 left and right), cannot be used in large flat-bottomed, arc-shaped bottom or other types of tanks, and the solid content of sodium aluminate solution is also limited within 600-700g / l, and the slurry flow rate also has special requirements, so its The scope of application is greatly limited, and it cannot meet the requirements of the current development of seed crystal decomposition technology for large capacity (4000M 3 above), high solid content (800-1000g / l) decomposition equipment requirements, and because the invention completely cancels the stirring, it is easy to produce a large amount of accumulated material at the bottom of the seed separation tank, causing sinking accidents and interrupting the production process

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