Co-treatment of copper electrolytic sludges and copper scraps for the recycled utilization of copper and arsenic.

The Cu electrolytic sludge is a hazardous waste because of its high Cu and As contents. In contrast, As content in Cu scraps is low but causes massive floating slime to be formed during its electrolytic refining, thus decreasing quality of the obtained cathode Cu. In this study, an innovative process was developed to transfer As from the electrolytic Cu sludge into Cu scraps, realizing the recycled utilization of As and Cu from them. The Cu electrolytic sludge was firstly subjected to oxidization roasting in the presence of Ca(OH)2, where the As2O3, Cu3As, and elemental As from the sludge were oxidized and immobilized into Cu3(AsO4)2 and Ca3(AsO4)2. The Cu3(AsO4)2 and Ca3(AsO4)2 retained in the roasted residue. The As volatilization efficiency was only 3.7% under the optimized roasting condition. In the next co-fire-refining of the roasted residue and Cu scraps, the As in Cu3(AsO4)2 and Ca3(AsO4)2 was reduced and transferred into the refined Cu at a content of 0.17 wt%. Although a volatile As2O3 could be generated in this co-fire-refining, the molten Cu scraps restricted As volatilization by forming a Cu-As alloy. With the obtained As-containing refined Cu used in electrolytic refining, the formation of floating slime could be decreased and consequently the quality of the cathode Cu would be increased. This research provided an alternative technology for Cu and As recycling by co-treating Cu electrolytic sludges and Cu scraps.

An approach of cobalt recovery from waste copper converter slags using pig iron as capturing agent and simultaneous recovery of copper and tin.

Massive amounts of waste copper converter slags have been produced from pyrometallurgical extraction of copper from copper concentrates, and the disposal of them in landfills creates serious environmental problems. However, this converter slag contains numerous valuable heavy metals, including copper, cobalt and tin etc. In this research, due to similar properties of iron and cobalt, pig iron with a low melting point was creatively used as capturing agent for cobalt recycling in a smelting reduction. The recovery of copper and tin was also studied. The phase transformation during reduction process was clarified by X-ray diffraction and Scanning electron microscope-energy dispersive spectrometer analyses. After the reduction performed at 1250 °C, the copper, cobalt and tin were recovered in a copper-cobalt-tin-iron alloy. The addition of pig iron improved cobalt yield, which was ascribed to the enrichment of cobalt in an iron-cobalt alloy phase. This decreased activity of the reduced cobalt and promoted reduction of cobalt oxide. As a result, the cobalt yield had a significant increase from 66.2% to 90.1% by adding 2% pig iron. Similarly, the copper also accelerated tin recovery through the formation of a copper-tin alloy. The copper and tin yields reached 94.4% and 95.0%, respectively. This work provided a high efficiency method to recover copper, cobalt and tin from waste copper converter slags.

Treating waste with waste: Metals recovery from electroplating sludge using spent cathode carbon combustion dust and copper refining slag.

Electroplating sludge is a hazardous waste and secondary metal resource because of its heavy metal content, which poses a huge threat to environmental safety if not properly disposed. An innovative process of oxidizing roasting followed by water leaching and smelting reduction to recover Cr, Cu, and Ni from electroplating sludge was proposed in this research, in which other two hazardous wastes of spent cathode carbon combustion dust and copper refining slag were co-treated. The NaF from spent cathode carbon combustion dust could convert Cr2O3 to Na2CrO4 using the oxidizing roasting process, resulting in a Cr recovery through the subsequent water leaching. The Na2CrO4 formation was promoted by CaO owing to it transferring the Cr spinel phase of FeCr2O4 [1+] to CaCrO4 and then to Na2CrO4. Under optimal conditions, the Cr recovery reached 97.1 %, and most 'F' was solidified into CaF2. In the next smelting reduction of the leaching residue, the Cu and Ni were recovered mainly in the form of Cu-Ni alloy. The addition of copper refining slag promoted their recovery, due to it modifying the molten slag and alloy structures and increasing the Cu-Ni alloy separation from molten slag. Some generated high-melting-point Cu-Ni-Fe and Ni-Fe alloys were converted to a Cu-Ni alloy with a low melting point in presence of Co from the copper refining slag, simultaneously with which the Fe was transferred out from Cu-Ni-Fe and Ni-Fe alloys and combined with Co to form a Fe-Co alloy. It increased Cu-Ni alloy droplets aggregation from molten slag and decreased their contents in the residual slag. Under optimized conditions, the Cu and Ni contents in the residual slag decreased to 0.37 and 0.06 wt%, respectively. Besides, the residual slag mainly composed of CaO, CaF2 and SiO2 could be used to prepare building materials rendering it harmless.