Research On Arsenic Phase Transformation And Control Mechanism In Copper Matte

With the depletion of high-grade copper ores,a large amount of low-grade and high-arsenic copper ores will become one of the main raw materials for copper smelting in the future.The high-arsenic raw materials will not only seriously affect the normal operation of copper smelting system,but also pose a great threat to the ecological environment.How to effectively control the migration and transformation of arsenic in copper smelting process is the key to the green development of copper smelting.Copper matte is an important intermediate product in copper pyrometallurgy process.The arsenic content in matte affects the efficiency of copper electrorefining directly.Based on finding out the occurrence characteristics of arsenic phase in copper matte,the paper elucidates the formation law of the key phase of arsenic in copper matte which is difficult to be decomposed,reveals the formation and decomposition mechanism of Cu-As alloy phase in high temperature process,and develops the new control technology of arsenic in matte on the basis of sodium salt regulation,and has made the following research achievements:（1）The occurrence characteristics of arsenic in copper matte were analyzed,which provided data for the directional regulation of arsenic in copper matte phase.The main phase of copper matte is bornite phase composed of cuprous sulfide and ferrous sulfide.The higher the grade of copper matte,the higher the arsenic content.The chemical states of arsenic in copper matte are in the order of residue arsenic,arsenate,arsenic sulfide and arsenic oxide.Most arsenic is in residue state and is very stable.In copper matte with high arsenic content,arsenic forms complex intermetallic compounds mainly by means of metallic bonding.By means of scanning electron microscopy（SEM）and backscattered electron analysis（MLA）,it is found that arsenic mainly exists in bornite phase,magnetite phase,copper-based alloy phase and other alloy phases.Among them,the copper-based alloy compound phase contains the largest amount of arsenic,and its arsenic concentration is about 1%-10%,and the arsenic distribution ratio is 60%-80%.Because the metal bond between Cu-As is extremely stable,it is difficult to separate arsenic at high temperature,which is the key of arsenic control in copper-based matte.（2）The formation mechanism of Cu-As alloy compounds in copper matte and the effect of smelting conditions on the residue of Arsenic in copper matte are revealed.Arsenic reacts with cuprous sulfide phase in copper matte under oxidizing atmosphere to form residual arsenic phase-Cu3As phase,which is the key reason for the residue of Arsenic in copper matte phase.The formation mechanism of Cu-As alloy compounds in copper matte and the effect of smelting conditions on the residue of Arsenic in copper matte are revealed.Arsenic reacts with cuprous sulfide phase in copper matte under oxidizing atmosphere to form residual arsenic phase-Cu3As phase,which is the key reason for the residue of Arsenic in copper matte phase.High temperature,proper oxidizing atmosphere and high grade of copper matte promote the formation of Cu₃As phase,while excessively high oxygen concentration will inhibit the formation of Cu₃As phase.When Arsenic reacts with cuprous sulfide at high temperature,it is preferentially enriched in the copper phase,and less in the cuprous sulfide phase.The experiments on the effect of smelting conditions on the dissolution of arsenic in the copper matte system show that the increase of smelting temperature,the reduction of reaction time and the increase of copper matte grade will promote the retention of arsenic in the copper matte system,and the copper matte system needs proper oxidation atmosphere and the existence of cuprous sulfide phase to produce elemental copper phase,which reacts with arsenic and fixes it in the copper matte system.Excessive oxygen and Fe₂O₄ can produce Cu-Fe spinel in copper matte system,inhibit the formation of copper element,and reduce the retention of Arsenic in copper matte system.（3）The mechanism and process characteristics of sodium carbonate transforming Cu-As alloy were clarified,and the effect of smelting conditions on the transformation of residual arsenic in Cu-As matte with sodium carbonate was studied.The Cu-As structure in Cu-As alloy is destroyed by sodium carbonate and oxygen and transformed into elemental copper and sodium arsenate/sodium arsenite.The newly formed sodium arsenate resists peroxidation on the surface of the copper-arsenic alloy.Under the experimental conditions of 8 wt.%sodium carbonate,reaction temperature 1250℃and reaction time 60 min,more than 98%of arsenic in matte was transformed to non-residual form.The effect of sodium carbonate on arsenic transformation in copper matte was studied.At the addition of sodium carbonate from 0 to 1 wt.%,sodium carbonate can effectively lower the melting point of the reaction,enhance the fluidity of the sample,and thus increase the oxidation atmosphere of the reaction system,and promote the decomposition and oxidation of bornite phase in copper matte.When the addition of sodium carbonate reaches 2 wt.%,sodium carbonate plays two roles in the transformation of arsenic phase in copper matte.Firstly,sodium carbonate can form a layer of sodium salts on the surface of copper matte,which can reduce the oxidation reaction of copper matte with air and hinder its decomposition and oxidation.On the other hand,copper-arsenic alloy phase in copper matte can be transformed into sodium arsenate phase by the action of sodium carbonate,completing the transformation from residue state to non-residue state.（4）The reaction mechanism of fayalite copper slag with sodium arsenate at high temperature was explored.In the reaction process of sodium arsenate with fayalite,there were both volatilization reaction（70wt.%）and dissolution reaction（30 wt.%）.Under the action of sodium arsenate,the silicate network structure of fayalite was destroyed and Fe O and Si O₂ were released.Si O₂ combined with Na₂O to form Na₂O·Si O₂（amorphous）,and Fe O reacted with[As O₄]to form arsenic and amorphous tetrahedron of iron oxide（[Fe O₄]）,which transformed part of the crystalline iron silicate into amorphous iron silicate glass.The volatilization reaction of sodium arsenate was the main reaction in this process.After the non-volatilized sodium arsenate enters into the structure of fayalite,the transformed[Si O₄]in fayalite and[As O₄]dissolved in fayalite phase combine through bridging oxygen bonds to form a new network structure,and the relative content of（Q²+Q³）in amorphous fayalite-type glass body reaches 41.12%,which enhances the stability of fayalite structure.The leaching toxicity test of the samples showed that the leaching toxicity of arsenic before and after the reaction of fayalite and sodium arsenate was reduced from 3025.52 mg/L to 12.8mg/L,and fayalite could effectively reduce the toxicity of sodium arsenate.