| The dispersive distribution,cyclic accumulation and the safe recycling of arseniccontaining wastes are the technical problems that must be addressed immediately in flash copper smelting process.It is beneficial to the development of source reduction,process control and tail-treatment technology of arsenic in copper flash smelting system.It reduces the vicious cycle of arsenic-containing intermediate materials in smelting systems by accurately analysing the occurrence characteristics and fine chemical structure of arsenic in copper smelting materials,products,and waste slag/tailing,studying the partitioning-circulation mode,and studying the speciation transformation mechanism of arsenic in the flash copper smelting process.It put forward harmless disposal and resource recycling methods for arsenic-containing tailings,which have important significance for the green and sustainable development of the copper pyrometallurgy industry.In this study,we focused on arsenic in the copper flash smelting system using synchrotron radiation X-ray absorption spectroscopy,X-ray diffraction technology,Xray fluorescence spectroscopy technology,the Tescan integrated mineral analyzer,an optical microscope,an electron probe,a scanning electron microscope,energy spectroscopy,and other microbeam and mineral analysis techniques.Environmental science,mineralogy,environmental chemistry,and trace element geochemistry were used to analyze the source composition and distribution-circulation mode of arsenic in the flash copper smelting process.The formation mechanism of arsenic-containing dust particles along the flue gas cleaning path,the factors affecting the separation of copper and arsenic in the process of copper slag beneficiation,and the occurrence characteristics of arsenic in the environment were also studied.The potential environmental risks of harmful trace elements in copper smelting discard tailing were assessed,and the comprehensive recovery of valuable elements such as molybdenum in the tailings and the removal methods of harmful trace elements were explored.The main conclusions were as follows:(1)The whole production process tracking sampling and systematic analysis of the copper flash smelting system were carried out to find out the source composition and occurrence characteristics of arsenic in the copper flash smelting system,and to clarify the distribution-circulation mode of arsenic in the copper flash smelting system.The results showed that 84%of the input arsenic in the flash smelting system came from the recycled materials,and 69%of the output arsenic was involved in the arsenic cycle in the smelting system.The remelting of mixed dusts and copper slag concentrate was the main cause of arsenic accumulation in the flash smelting system.And the smelting production process was the key to arsenic balance control and arsenic pollution prevention of the copper flash smelting system.The arsenic in slag-type recycled materials was mainly returned to smelting unit in the form of As(Ⅴ)-O,and the dusttype recycled materials contributes to both As(Ⅲ)and As(Ⅴ)in the mixed raw materials.The recycled materials played a decisive role in the composition of arsenic in the mixed raw materials.(2)The physical and chemical composition,particle size distribution,microscopic morphology,and fine structure changes of arsenic-containing mineral particles in different deposition positions along the flue gas cleaning path during flash smelting and blowing were compared.The formation mechanism of arsenic-containing soot particles along the flue gas cleaning path and the key factors affecting their deposition positions were also revealed.The findings indicate that the arsenic concentration increases and the average particle size decreases gradually along the gas cleaning line.The contents of arsenic and copper in the dust are negatively correlated with their pH value,while the proportion of PM 10 in the ESP dust is as high as 95.02%.The arsenic in the flue gas tends to be concentrated in the fine particles,mainly in the form of oxidized-arsenic and arsenate-arsenic,and the trivalent arsenic oxides are mainly deposited in the waste heat boiler(WHB).The formation mechanism of arsenic-containing dust particles can be divided into mechanical formation mechanism(condensation deposition of As2O3 particles washed through the pipe wall)and chemical formation mechanism(deposition of non-volatile arsenate and arsenite compounds generated by chemical reactions).Arsenic deposition location and arsenic chemical composition are affected by temperature,initial arsenic content and basic metal oxide content in flue gas cleaning system.Temperature plays a key role in the deposition location of As2O3.(3)The mineralogical composition and fine structure of arsenic in flash smelting furnace(FSF)smelting slag and its beneficiation tailings and concentrate were quantitatively analyzed,and the redistribution behaviour of mineral components and main trace elements in the process of sulphide flotation was revealed.The influencing factors of copper and arsenic separation in the smelting slag beneficiation process were discussed from the perspectives of mineralogy and morphology.The results show that arsenic,copper and cadmium tend to be enriched in the slag concentrate,while other elements are mainly discharged into the tailings.Arsenic in slag is mainly in the form of copper-arsenic alloys,which account for about 32%of the total copper-containing phases and about 89%of the total arsenic-containing phases,respectively.Arseniccopper alloys are closely embedded in the matte phase,which is the key phase affecting the separation efficiency of copper and arsenic.Arsenic in slag concentrate and tailings is mainly in the form of arsenate,and the distribution behaviour of the arsenic phase depends on the different embedded modes of the arsenic phase in slag concentrate and tailings.Arsenic in tailings is mainly distributed in silicate phase,and arsenic in slag concentrate is mainly embedded with copper sulfide.Inhibiting the recombination of Cu-S phase and arsenic oxide anion in the flotation process is helpful to reduce the enrichment rate of arsenic in the slag concentrate.(4)The content and occurrence form of arsenic in the tailings were clarified.Similarly,the eco-toxicity and environmental precipitation rule of arsenic in the tailings were revealed and the potential ecological risks and human health risks of arsenic in the tailings were evaluated.The results showed that the arsenic content in the tailings was 0.11～0.17%,and the pH value was 7.95～8.61.Arsenic was mainly in residues,accounting for 90～95%,with low bioavailability.The concentration of arsenic in the four leaching toxicity methods(HJ/T299—2007-sulfuric acid and nitric acid method,HJ557—2009-horizontal oscillation method,TCLP method,EN12457-3-European Standard)was much lower than their respective limits.In the leaching process,the tailings have a strong pH buffering capacity.The environmental precipitation of arsenic mainly occurred in the early leaching stage and formed a dynamic equilibrium in the middle leaching stage.The risk assessment code(RAC)of arsenic in tailings was lower than 1%,indicating a risk-free level.Arsenic in tailings did not pose non-carcinogenic or carcinogenic health risks to exposed populations.(5)The phase composition of the tailings was divided into four types:magnetite/hematite,silicate,metal sulfides and oxides,and other phases.The occurrence pattern of molybdenum in different mineral components of the tailings was revealed,and a method of separation and pre-enrichment of molybdenum and copper resources and removal of environmentally harmful elements was proposed.The results show that Mo is adjacent to magnetite/hematite-Fe,and S distributions.After magnetic separation,the contents of arenic in non-magnetic slag decreased(the reduction rates were(58～60%).Molybdenum and copper were significantly enriched in the magnetic products,with enrichment rates of 34～41%and 15～21%,respectively. |
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