The Research On Harmless Treatment And Comprehensive Utilization Of Chromium Slags

The harmless treatment and comprehensive utilization of chromium slags are not only the requirement for environmental protection and healthy development for many companies,but also a hot issue in solving the problems in hazardous waste storage.Because chromium salt is a widely used chemical product,its output accounted for around one-third of global manufacturing.The storage of chromium slags,which are the by-products of chromium salt manufacture,are about 5 million tons.During the detoxification of chromium slags,Luliang chemical industrial company has actively involved in chromium slags detoxification.This company has built many production lines for detoxification,such as the mechanical semi-dry method and dry-process rotary kiln.This company is looking for the method of comprehensive utilization-detoxification of chromium slags,and has accumulated lots of valuable experiences.The main research findings are as follows:The technique parameters for mechanical semi-dry detoxification include:r aw materials ground to 0.08 mm,calcination temperature above 1000 ℃,chro mium slags mix with 10%to 12%.The intake air volume should also be adju sted for rapid cooling and oxidization.The control conditions for the method of dry-process rotary kiln are according to the mix percentage of 100:20 for chromium slags and bunker coals,which are 7.5%moisture content and 10%moisture content,respectively.Chromium slags accounted for 83%and bunker coals accounted for 17%.If the exhaust fume of 200 ℃ was taken as the drying medium,the particle size will drop to less than 6 mm.In order to restore the detoxification process,the ground particles not only need to contact with high temperature air,but also need to heat to above 950 ℃ with the reducing flame of special coal injection pipe.Finally,detoxified chromium slags need to be rapidly cooled with fresh water or green vitriol which contains sulfuric acid.High temperature smelting reduction sintering method can thoroughly realize the harmless treatment of chromium slags,which includes the stages of restoration and high temperature smelting.If we use the chromium slags for sintering and iron-making technology,the production of iron slags will increase 1.8%～3.6%per ton.Although it increases the slags,it will not bring obvious effects on the blast furnace ore.Because blast furnace smelting alkali metal can bear a load for 1 to 2 kg of iron slags,so it is in the control of its bearing capacity.The mechanical shaft kiln poisonous slags’ hexavalent chromiumm is all below standard of 1.5mg/L,however during the practical measure of hexavalent chromium,the monitoring scope is 0.004-0.147 mg/L.There are no hexavalent chromium monitoring results using the method of rotary kilndetoxification.Lixivium,sintering dust and blast furnace dusting ash’s hexavalent chromium and all chromium of high temperature smelting reduction sintering method are respectively L(not detected)to 0.163 mg/L,L(not detected)to 0.337 mg/L.All the three methods’ the hexavalent chromium and all chromium are both far below the corresponding standard limit of"Identification Standards for Hazardous Wastes(Identification for Extraction Toxicity)".It’s also below the maximum acceptable emission concentration of"Integrated Wastewater Discharge Standard" and "Chromium Slag Pollution Environmental Protection Technical Specifications(tentative specification)" which is in the Appendix D.According to the thinking routing of reducing,reusing,integrating and handling the chromium slags,we can build five stages of management system for the handling of chromium slags,and finally accomplish the comprehensive utilization of chromium slags.