| China is one of the country that possesses considerable quantities of Asbestos mineral resource, and it's resource reserves of asbestos mineral rank 3rd in the world. West China is the major mineral area of asbestos. Asbestos mining rate is not high, the exploiting process of asbestos can produce a large number of asbestos gangue , except a few gangues can backfill, majority of them have to take up place and be stacked, thus they heavily pollute environment and threaten human health. As the gangue of asbestos contain lots of useful components, it is necessary to recycle gangues of asbestos for environmental protection and rational use of resources .Currently in China,methods about preparation of light MgO with asbestos gangue can be divided into hydrochloric acid and sulfuric acid method, but these methods have many problems, such as high costs, low raw material conversion , improper disposal of waste, too waste of resources and low quality of magnesium products. In this paper, according to the feature of high magnesium content of asbestos gangue in Sichuan Province, and based on the study at home and abroad , we designed a process route of clean production in closed circulation, and proposed that concepts and requirements of clean production should applid to the whole production process , we developed new reagent of iron removal to ensure the purity of light MgO product. This process integrated production costs, energy consumption and efficiency with eco-environmental factor, intended to eliminate pollution from production source to production process, make waste reducing, recycling and become harmless, to achieve efficient, clean, comprehensive utilization of valuable component of asbestos gangue .Main contents and conclusions of this paper is as follows:(1)Determination about the optimum conditions of leaching Magnesium from ore sample. Leaching of magnesium from ore is the most critical process technology, it's necessary to screen the process conditions rigorously . Following the principle of Low consumption of cleaner production material, we did comparative study of conditions , such as ore particle size, acid type and amount, liquid to solid ratio, leaching time and addition of cosolvent . We considered the leaching rate of magnesium as indicator, determined the optimal conditions : 80 mesh ore, liquid to solid ratio of 4:1 premised, after 1hour immersed in 120% sulfuric acid and 1% cosolvent acid environment , magnesium leaching rate from ore is up to 98.76%, more feasible than previous studies of the conditions(2)Research and development about multi-effect separation agent for impurities. After leaching , the crude sulfate solution contains iron impurities, if do not remove iron impurity , it will cause phenomenon of iron oxide red . as Iron precipitator, Ammonia and Sodium hydroxide are not ideal , and they will pollute environment and corrode equipment of operation. To solve this problem, , we developed new and more effective reagent of separating impurity from the perspective of clean production. We toke the rate of iron removal as reference, and compared the new with the two previous reagents. the result shows that the separation rate of multi-effect dose is up to 99.94% , without phenomenon of iron oxide red, this new reagent achieved goal of cleaner production.Therefore, multi-effect separation reagent was determined as the best precipitant, and optimal pH value of multi-effect separation reagent was between 5.5 and 6.5 .(3)Selection conditions for preparation of light MgO. Our experiment choosed powder, slurry and clarified liquid of sodium carbonate as study object to find out optimal precipitation mode and the best aging time . When precipitate was formed then dried, temperature and time of calcination were of optimal choice. the solution by adding Na2CO3 clarified liquid completely reacted, after immediate filtration without aging, the product of highest purity was obtained in 850℃calcination in 2.5h. Washing with hot water is the key procedure to quality of MgO. After the recovery of by-products, there is no interference in waste liquid, that can be used as industrial water back to mother liquor, thus this process reflected the characteristics o closed loop technology and clean production in the eradication secondary pollution, reduced load of end processing(4)Measurement and Analysis of quality of MgO product to ensure the desired purity. XRD characterization showed very sharp peaks with high purity; SEM characterization showed that particles morphology were spherically distributed; Chemical analysis and atomic absorption method for quantitative analysis showed that MgO content was more than 95%, archieved the desired effect, Impurity CaO content was 0.17%, iron is only 0.0055%, ignition loss was 3.14%, according to HB / T 2573-94 the division criterion of industrial grade MgO, the product achieved superior level. As a raw materials of refractory, high-purity MgO has a promising prospect of application in refractory field.(5)Simple cost estimation and benefit analysis of whole process for proving that process of clean production in MgO preparation is the environmentally friendly, economically advantageous technology.The process is simple, environmentally friendly, it can produce high purity, low impurity content products, and its by-products can be used for extensive fields also. It provides a resource approach for the preparation light MgO to asbestos gangue , and coordinating development of production with environmental issues, this process is the specific application for the clean production, utilization of waste, recycling economy and sustainable development that our nation always advocate.
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