Copper Bioleaching Of Waste Printed Circuit Boards And Study On Photocatalytic Properties Of CuFe₂O₄

With the increasing level of science and technology,as well as human’s quest for high-quality life,the life span of electronics and electrical equipments are reduced by degerees.Among them,acts as the core component of electronic and electrical equipment,the waste of printed circuit board（WPCBs）is increasing in numbers every year.Compared to traditional WPCBs disposal processes,bioleaching treatment has aroused more importance to scholars globolly due to its environmental protection,simple operation and environmental friendliness.Based on the mixed system composed of three kinds of bacteria:Acidithiobacillus thiooxidans（A.t）,Acidithiobacillus ferrooxidans（A.f）and Leptospirillum ferriphilum（L.f）,we used the direct leaching method to recycle Cu from WPCBs,and optimized the leaching conditions.Aiming at solving the problems of long time direct leaching period and its’low efficiency,we also proposed a calcination pretreatment coupled indirect bioleaching technological means,thus effectively improving the recovery efficiency of the overall process,meanwhile make Cu containing biological leachates into highly photocatalytic and easily recyclable photocatalytic materials through coprecipitation hydrothermal method.The main conclusions are as follows:（1）The WPCBs metal species were complex and varied with a high content of Cu（mainly monomorphic）,which accounted for 22.51%.Its main morphological proportion of occurrence are:oxide bound（76.7%）,acid solution（15.4%）,sulfide and residue（4.6%）and organic bound（3.3%）.Thermogravimetric analysis of WPCBs showed that the mass of WPCBs decreased sharply with the increasing temperature.When temperature hits 600℃,the residual state of copper was removed completely with the mass loss about 39%.（2）The mixed systems of three bacteria strains grew and propagated faster than the single strain system.After seven days culture,the bacterial concentration of the mixed reached 3.4×10~8/m L,p H dropped to 0.8 and Fe³⁺concentration attained 1936.7 mg/L,which meet the basic requirements of biological extraction.Under the optimal reaction conditions:solid-liquid ratio 1%,the initial p H value 0.8,temperature 35°C,shaker speed 135 rpm,Cu was completely leached after 11 days,which verified that the mixed bacterial system could effectively recycle Cu from WPCBs.We also tested the efficiency of four types of copper leaching systems:direct leaching（100.0%）,indirect leaching（48.2%）,H₂SO₄+Fe³⁺leaching（44.6%）,and H₂SO₄ leaching（18.1%）under the same optimal conditions,the results indicated that the leaching mechanisms of copper were not just the function of H⁺and Fe³⁺simply,microorganisms also played a crucial part.（3）The pretreatment of WPCBs by low-temperature calcination can effectively improve Cu in its’enrichment degree and the occurrence form,the enrichment degree of Cu was positively correlated with temperature.XRD and XPS analysis showed that the amount of Cu O increased significantly at 400℃,but Cu was not completely oxidized.There was no elemental Cu at 600℃and 800℃,indicating that Cu has been completely oxidized;sintering obviously occured at 800℃,leading to the decomposition of Cu O and the formation of Cu₂O,which was not conducive to bioleaching.The physicochemical analysis of roasting slag showed that 600℃was the optimal roasting pretreatment temperature.The biological indirect leaching roasting slag experiment was designed by response surface methodology（RSM）,and the optimal conditions were obtained as follows:the solid-liquid ratio was 4.37%,the initial p H value was 0.83,the temperature was 30.19°C,and the shaker speed was 141.79 rpm.After 24 h,Cu in WPCBs can be 100%leached,which confirmed that low-temperature roasting pretreatment coupled with biological indirect leaching can effectively shorten the leaching period and improve the leaching efficiency.（4）Using ammonia water as precipitant,the copper-containing leaching solution was directly prepared into Cu Fe₂O₄（B-CFO）by co-precipitation-hydrothermal method.Compared with the pure chemical Cu Fe₂O₄（C-CFO）prepared by the same method,both materials can be excited under visible light,and the light response range of B-CFO is narrower than that of C-CFO.The recombination rate of the photogenerated electron-hole pairs is slower,and the signal peaks of·O₂^-and·OH are significantly stronger than those of C-CFO;this leads to a higher photocatalytic performance of the material.Under visible light for 180 min,the degradation rates of methylene blue by B-CFO and C-CFO were 93.1%and 82.8%respectively.Both materials have high cyclic photodegradation activity and after five cycles,the degradation rates of B-CFO and C-CFO can still reach 84.6%and 77.5%.