(School of Chemistry and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083)
First, the content introduction
Ultrafine magnesium hydroxide and ultrafine silica with high specific surface area were prepared by acid leaching, filtering and washing, controlling alkali precipitation of magnesium hydroxide, alkali dissolution of acid leaching residue, filtering and washing, and controlling precipitation of silica by dilute acid method, and surface treatment or surface modification were carried out in time during alkali precipitation and dilute acid precipitation. The main features and innovations are:
1) creatively integrates the technical principles of chemical leaching separation technology, powder surface treatment technology and product particle size and morphology control technology, making asbestos tailings resource and harmless, promoting the utilization rate of asbestos ore, and solving the pollution problem of asbestos tailings well.
2) removing iron impurities from the leaching solution by oxidation and alkali precipitation; The entrainment rate of magnesium hydroxide in iron hydroxide is reduced by precipitating iron hydroxide with dilute alkali and washing and filter pressing the filter cake. In the process of magnesium hydroxide precipitation, the particle size of precipitation is controlled by timely surface treatment to prevent the particles from forming hard aggregates during aging and drying.
3) alkali dissolving the filter residue after leaching magnesium salt to remove impurities; Precipitating ultrafine silica with dilute sulfuric acid: Particle size control (barrier) agent is used to adjust the particle size and specific surface area of the product to prevent the particles from forming hard aggregates during aging and drying, so that the particles have good dispersibility.
Technical indicators of main products in pilot test:
Ultrafine magnesium hydroxide: median particle size (d50) (1.0 0.2) micron, Mg (OH) 2 = 98% 0.5%, whiteness > 92.0.
Ultrafine silica: BET specific surface area 190 ~ 479m2/g, pore volume 0.47 ~ 0.47 ~1.01cm3/g/g, average pore size 30 ~ 80 nm, dry silica content ≥99%, whiteness ≥ 93.
Output rate (calculated by treating 1000 kg tailings): superfine magnesium hydroxide ≥420 kg, superfine silica with high specific surface area ≥3 10 kg, and the recovery rate of magnesium oxide and silica in tailings is over 80%. It is particularly important that the pilot test results (magnified by 2800 times on the basis of laboratory tests) are obviously better than those of laboratory tests and have good repeatability.
Second, popularization and application
The main products of the project (high purity superfine magnesium hydroxide and high specific surface area superfine silica) are low-smoke, non-toxic, environmentally friendly, and have good filling performance, which has a good market prospect in the field of flame retardant materials.
At present, Aksai County, Gansu Province is building an efficient comprehensive utilization production line with an annual treatment capacity of 20,000 tons of asbestos tailings (the first batch of national debt substitution projects for resource conservation and environmental protection by the National Development and Reform Commission in 2007).
Three. Identification, awards and patents
In February 2005, it passed the appraisal of technical achievements organized by the Ministry of Education. The invention patent has been obtained with the patent number ZL03 157398.3 (authorization announcement date: 2005 1 1.2). It was awarded "Top Ten Excellent Patents in Gansu Province during the Tenth Five-Year Plan" by the Intellectual Property Commendation Committee composed of Science and Technology Department, Personnel Bureau and Intellectual Property Office of Gansu Province.