Yasushi Takasaki

Treatment of smelting residue for arsenic removal and recovery of copper using pyro-hydrometallurgical process.

During pyro-metallurgical processing of non-ferrous metals, smelting residues such as smelter slag, flue gas, containing value metals and also harmful substances are inevitably generated as secondary product. For reduction of environmental loading and recovery of the value metals, such materials demand proper treatment options. In this research, some experimental steps were investigated to remove high arsenic (As: 19.5 wt%) and recover copper (Cu: 3.1 wt%) contained in such smelting residues. In the first-stage arsenic and other volatile materials were removed by pyro-metallurgical treatment and in the second-stage the treated residue from pyro-processing was treated in hydrometallurgical processing involving a two-stage leaching operation in H(2)SO(4) solution to dissolve the metals followed by solvent extraction using LIX-84I as extractant to recover dissolved Cu in final leached solution. The results showed that over 90% of arsenic in smelting residue was removed by volatilization and recovered as As(2)O(3) while copper content increased to 4.2 wt%. In the two-stage leaching process, first up to 90% of arsenic was selectively dissolved in 0.25 mol/L H(2)SO(4) solution and second, the solids were further leached in 1.0 mol/L H(2)SO(4) solution giving 85% of copper dissolution. Over 90% of copper dissolved into solution was recovered by solvent extraction. Finally over 99% of arsenic dissolved in the first-stage leach solution was co-precipitated with iron dissolved in second-stage leach solution after copper recovery.

Control of metal toxicity, effluent COD and regeneration of gel beads by immobilized sulfate-reducing bacteria

Over the last few decades, the use of sulfate-reducing bacteria (SRB) in the treatment of heavy-metal containing wastewaters including acid mine drainage has become a topic of scientific and commercial interest. However, technical difficulties such as the sensitivity of SRB to toxic metals and high effluent COD limit the widespread use of SRB in high heavy-metal containing wastewater. The aim of this study was to clarify the reasons why the immobilized SRB sludge with inner cohesive carbon source (ISIS) process can endure high metal toxicity and decrease effluent COD. The ISIS process can physically set apart SRB and free the system of external influences such as the surrounding toxic metallic ions, as well as form inner carbon sources to avoid high effluent COD. Metal toxicity and bead durability are the two major factors which influence the regeneration and reuse of gel beads. Reuse of suspended SRB sludge and beads crosslinked with boric acid were unsuccessful due to metal toxicity and agglomeration of beads, respectively. However, beads crosslinked with ammonium sulfate prevented agglomeration of beads allowing successful bead regeneration and reuse. The result of four cyclic trials showed that over 99% of zinc was removed in each trial using these beads.

Copper Recovery from the Mine Tailings by Combination of Flotation with High-Pressure Oxidative Leaching and Solvent Extraction

The aim of this research was to develop a copper recovery process from mine tailings (0.34%Cu) using flotation followed by high-pressure oxidative leaching (HPOL) and solvent extraction. The results of HPOL using the concentrate of mine tailings obtained by flotation under the optimal conditions of the previous study shown that an efficient copper dissolution of 94.4% was achieved in an H2O media, while the copper concentration of PLS reached to be 2.9 g/L. The solvent extraction of PLS obtained from the optimal HPOL showed that 91.3% copper was recovered in stripped solution under the determined optimum conditions, in which the copper concentration achieved to be 44.8 g/L. Finally, a proposed copper recovery process from the concentrate of mine tailings was developed by combination of HPOL and solvent extraction, while a total copper recovery of 86% was achieved.

Development of copper recovery process from flotation tailings by a combined method of high‒pressure leaching‒solvent extraction

Sulfide copper mineral, typically Chalcopyrite (CuFeS2), is one of the most common minerals for producing metallic copper via the pyrometallurgical process. Generally, flotation tailings are produced as a byproduct of flotation and still consist of un‒recovered copper. In addition, it is expected that more tailings will be produced in the coming years due to the increased exploration of low‒grade copper ores. Therefore, this research aims to develop a copper recovery process from flotation tailings using high‒pressure leaching (HPL) followed by solvent extraction. Over 94.4% copper was dissolved from the sample (CuFeS2 as main copper mineral) by HPL in a H2O media in the presence of pyrite, whereas the iron was co‒dissolved with copper according to an equation given as CCu = 38.40 × CFe. To avoid co‒dissolved iron giving a negative effect on the subsequent process of electrowinning, solvent extraction was conducted on the pregnant leach solution for improving copper concentration. The result showed that 91.3% copper was recovered in a stripped solution and 98.6% iron was removed under the optimal extraction conditions. As a result, 86.2% of copper was recovered from the concentrate of flotation tailings by a proposed HPL‒solvent extraction process.

Immobilization of Hexavalent Chromium in Stainless Steelmaking Slag

Chromium is an essential element which contributes to our life activity. However, since the hexavalent chromium causes health damage, its content in water is strictly limited below 0.05 mg/L as the aqueous and soil environment standard values in Japan. The development of high-efficient stabilization method of the steelmaking slags containing chromium is urgent in order to utilize the slags to civil engineering works. In present work, the elution behavior of chromium from stainless steelmaking slags was clarified. Then, a principle of prevention of hexavalent chromium formation and chromium immobilization by the hydrate formation was discussed.

Removal of Fission Products in the Spent Electrolyte Using Iron Phosphate Glass as a Sorbent

This study is carried out to make the pyroprocessing hold a competitive advantage from the viewpoint of environmental load reduction and economical improvement. As one of the measures to reduce the volume of the high-level radioactive waste (HLW), the phosphate conversion method is applied for removal of fission products (FP) from the melt, referring to the spent electrolyte in this paper. Among the removing target chlorides in the spent electrolyte i.e., alkali metals, alkaline earth metals and rare earth elements, only the rare earth elements and lithium form the precipitates as insoluble phosphates by reaction with Li3 PO4 . The sand filtration method was applied to separate FP precipitates from the spent electrolyte. The iron phosphate glass (IPG) powder, which is a compatible material for the immobilization of FP, was used as a filter medium. After filtration experiment, it was proven that insoluble FP could almost be completely removed from the spent electrolyte. Subsequently, we attempted to separate the dissolved FP from the spent electrolyte. The IPG was being used once again but this time as a sorbent instead. This is possible because the IPG has some unique characteristics, e.g., changing the valence of iron, which is one of its network modifiers due to its manufacturing temperature. Therefore, it would be likely to sorb some FP when the chemical condition of IPG is unstable. We produced three kinds of IPG under different manufacturing temperature and confirmed that those glasses could sorb FP as anticipated. According to the experimental result, its sorption efficiency of metal cations was attained at around 20–40%.Copyright

Separation of Lanthanoid Phosphates From the Spent Electrolyte of Pyroprocessing

This study is carried out to make the pyroprocessing hold a competitive advantage from the viewpoint of environmental load reduction and economical improvement. As one of the measures is to reduce the volume of the high-level radioactive waste, the phosphate conversion method is applied for removal of fission products from the melt as spent electrolyte in this paper. Though the removing target elements in the medium are alkali metals, alkaline earth metals and lanthanoid elements, only lanthanoid elements and lithium form the insoluble phosphates by reaction with Li3 PO4 or K3 PO4 . Therefore, as the first step, the precipitation experiment was carried out to observe the behaviours of elements which form the insoluble precipitates as double salts other than simple salts. Then the filtration was experimented to remove lanthanoid precipitates in the spent electrolyte using Fe2 O3 -P2 O5 glass system as a filtlation medium which is compatible material with the glassification. The result of separation of lanthanoid precipitates by filtration was effective and attained almost 100%.Copyright