| A large amount of arsenic wastewater is generated from bio-oxidation gold extraction process, which has the characteristics of strong acidity, high As and Fe content. Due to its strong corrosiveness toxity, the wastewater must be treated and then discharged after reaching the standard. At present, the commonly method used to deal with the wastewater by gold production enterprises is lime-molysite, which can form FeAsO4and then remove it.For a long time, the arsenic residue is just buried for economic and technology aspects. This is not only causing the potential of secondary pollution, but unable to reuse valuable elements, wasting seriously resources. So there have been significantly economic and social benefits to explore the technically feasible and economical treatment for arsenic wastewater to reuse the valuable elements.Taking the acidic arsenic bio-oxidation gold extraction waste water as the research object, this paper studied how to recycle the mainly valuable elements As, Fe and S by two different process, in order to realize the unity of safety, reduction and recycle. The main research contents and conclusions were as follows:1. Recovery of As and Fe:According to the theories of chemical deposition, the co-precipitation compound of arsenic and ferric ion was carried out using caustic calcined magnesia as precipitant to adjust pH value solution The effect of pH, mixing speed and temperature on the primary recovery ratio of arsenic and ferric were investigated. The co-precipitation compound was treated by NaOH and Na2CO3leaching to separate arsenic and ferric. The effect of craft conditions on separation efficiency of arsenic and ferric were investigated, such as pH, liquid-solid ratio, reaction time, temperature, excess sodium carbonate coefficient and aging time. The results showed that the appropriate craft conditions for co-precipitation of arsenic and ferric were pH3.5, mixing speed500rpm, reaction temperature25℃. Under these conditions, the primary recovery ratio of arsenic and ferric was99.56%and98.71%, respectively. The appropriate craft conditions for NaOH and Na2CO3leaching were excess sodium carbonate coefficient1.2, liquid-solid ratio6.5:1, reaction temperature80℃, reaction time2h and aging time1h. Under these conditions for secondary leaching, arsenic content in liquid was94.58%, and that in solid was0.17%. This is investigated that As and Fe in waste water were separated completely.2. High value utilization of As and Fe:The filter residues obtained from separation of arsenic and ferric was used to prepare transparent iron oxide red. The effect of calcinations temperature and time on quality of iron oxide red was investigated. The proper conditions for preparing iron oxide red were900℃and2h. The quality examination showed that the quality indexes fit to the standard of GB1863-89.Based on thermodynamic analysis, the recovery of arsenic from sodium arsenate was studied using hydrazine hydrate as reduction agent under the condition of ultrasonic. The effect of craft conditions on arsenic recovery rate was investigated, such as dilution multiple, pH, excessive hydrazine hydrate coefficient, temperature and ultrasonic intensity The optimum conditions were pH7.0, temperature80℃, ultrasonic intensity160W. Under these conditions, the recovery rate of arsenic was62.9%.40%sodium hypophosphite was used for secondary recovery and the arsenic recovery was up to91.77%.The results showed that the recovery method of arsenic was feasible, which was environmentally metallurgical process for preparing As without generating AsH3.3. Dynamics of selective leaching of arsenic:According to equations of different rate controlling steps of thermodynamics of irreversible processes, the dynamics of different temperature and mixing speed were obtained. And activation energy and preexponential factor of different controlling steps were25.78kJ-mol-1and9.39, respectively.4. Dynamics of preparing As under ultrasonic:dynamics disciplinarian was investigated and dynamicsparameters were obtained. The equation wasAnd the relationship between k and temperature wasThe reaction energy was21.05kJ-mol-1, preexponential factor.A=0.15. The induction period was shortened and reaction rate was increased by ultrasonic. 5. The process of selectively recovery and high-value utilization of As, Fe, S: Fe ions in wastewater were recycled to phosphate ferric using PO43-compound as precipitant. Then the As and S in solution were recovered as copper arsenate and calcium sulfate, respectively. The effect of technology parameters on recovery rate of Fe, As, S was investigated. The results were as follows:(1) The optimum conditions for selectively recovering Fe were pH2.5, reaction temperature45℃, and mixing speed500rpm. Under these conditions, the recovery rate of Fe was99.83%, and the arsenic residue rate in liquid was98.64%, which suggests the effectively separation of arsenic and ferric.(2) According to thermodynamics of irreversible processes, the dynamics of selectively recovering Fe were investigated. The equations of different temperature and mixing speed were obtained. The relationship between reaction rate and affinity were also analysized. The results showed when mixing speed was above600rpm, the effect of diffusion was eliminated and the reaction rate was determined by affinity.(3) The optimum conditions for recovering As as copper arsenate were pH4.0, reaction temperature50℃, and mixing speed500rpm. The recovery rate of arsenic was95.1%, which suggests effective recovery of arsenic.The dynamics of preparing copper arsenate were investigated, and equations and relate parameters were obtained.The optimum conditions for preparing CaSO4whisker were reaction temperature120℃, slurry concentration7%, mixing speed400rpm. Under these conditions, the CSW aspect ratio was55and the Growth Mechanism was investigated. |
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