Study On Chromium Residue Detoxification By Energy-containing Waste Gas And Comprehensive Utilization Of Detoxified Chromium Residue

Chromium is one of the main inorganic chemical products and an important industrial raw material in China,which was widely used in the industry of metallurgy,leather,dyes,electroplating and so on.Industrial emissions of chromium slag contain high content of water-soluble hexavalent chromium Cr???in the form of sodium chromate,which could cause adverse effect on human health and the environment,and was listed as one of hazardous solid wastes by the state.The high cost of detoxification agents,secondary pollution and incomplete detoxification of chromium residue are the shortcomes in wet detoxification process.Microbial detoxification method usually needs long time and with small processing scale.Dry detoxification process is widely used in industrial production due to its simple operation,complete detoxification effect and large processing capacity,but it also has the problems of large investment and high energy consumption.Therefore,it is of great practical significance to seek an economical and efficient method of detoxification of chromium residue without secondary pollution.Basing on the principle of using waste treat waste,this thesis researches the method of chromium slag detoxification by energy-contaning waste gas.The laboratory simulation of energy-contaning waste gas is useded to detoxify chromium slage under the condition of high temperature,researches of mineral phase changing in the detoxification process,reaction mechanism,reaction kinetics analysis and limiting factors are implemented.The conventional detoxification process is optimized through additive selection and classification detoxification.Chromium slag after detoxification is utilized as cement mixed material and aggregate.Finally,pilot-scale processing has been accomplished,the technological and economical analysis were carried out.Specific research contents and conclusions are as follows:?1?Cr???most exists in the third class mineral crystal lattice,high temperature conditions could destruct the structure of Cr???containing minerals,and release the Cr???;The control link of chromium slag detoxification process is internal diffusion,thus,CO detoxification of chromium slag is mainly limited by temperature;Below 200?,bound water of some minerals dissociate,soluble and surface adsorpted Cr???is reduced,dynamics model is:???;Between 200 to 400?,Cr???-containing mineral structure was destroyed,Cr???was released and reduced,the dynamic model for the main reaction stage is???;Above 400?,mineral components keep losing oxygen,which has no effect on the detoxification of chromium residue.?2?The reaction conditions?reaction temperature,reaction time,capacity,gas flow rate and CO concentration,crushing particle size?affect the Cr???leaching and content in chromium slag.The effect of crushing particle size and gas flow is not obvious,the influence of main conditions range in a descending order is:the reaction temperature,the CO concentration,the reaction time,the processing capability;The optimized reaction temperature with response surface analysis method is about 390?,which is much lower than the traditional process temperature of chromium slag detoxification by carbon.?3?The material properties?H₂,CH₄ concentration,additives,particle size feature of chromium slag?affect the Cr???leaching and content in chromium slag.The reducing gases of less amount in the energy-contaning waste gases are H₂ and CH₄,H₂ can improve the efficiency of chromium residue detoxification,while CH₄ decreased the detoxification efficiency;Additives can further reduce the reduction Cr???leaching concentration and total Cr???content,the optimization ability ranged in a descending order is:MgO>FeO>Al₂O₃,with the increase of adding amount,the Cr???and total Cr???is reduced,adding 6¹0%MgO can reduce the temperature condition to 350?;The Cr???content in fine particle size of chromium slag particles is low,while in the coarse particle size Cr???content is higher,reaction temperature of detoxification pf fine particle size?0.053⁰.53 mm?,medium size?0.53⁵ mm?,and coarse particle size?5¹0 mm?chromium slag particles,are 300,350 and 400?,respectively.To achieve the standards of chromium slag pollution environmental protection technical of disposition of landfill standards,Cr???leaching concentration is lower than 1.5 mg/L.?4?In the industrial scale experiments,Cr???leaching concentration could be reduced to less than 1.5 mg/L under 400?,and be reduced to less than 0.5 mg/L under 500?;The detoxified chromium residue under 500?can be used as fine aggregate and mineral admixture material,and the strength property of cement is better than that of conventional concrete under appropriate proportion,which can meet the requirements of concrete strength of ordinary civil buildings.The Cr???in the chromium is further reduced slag by cement under the action of solidification,migration ability of Cr???was extremely weak,the effective diffusion coefficient is of less than 10^-9,leaching factor is above 9,the migration ability of Cr???is lower than that in the vitrification fixed chromium slag under high temperature.