This paper demonstrates the importance of comminution for achieving compositional liberation in order to establish an effective solid-solid separation process, in especial, in the field of mineral processing and resources recycling. We have developed a unique liberation model in comminution process by introducing an index of “preferential breakage probability”, e1, at phase boundary to the Wiegel model, which is well known in the field of mineral processing. From the results, we easily understood that the degree of liberation gradually increased with increasing the e1 and it could be demonstrated that the energy required for obtaining a certain degree of liberation dramatically decreased with increasing the e1. This calculation indicated the importance of preferential breakage at phase boundary in comminution with lower energy consumption, which could contribute better separation efficiency in the following solid-solid separation. In other words, the e1 must become a good index for the DfR (Design for Recycling) as an “EcoDesign” from the viewpoint of compositional separation. The paper also describes several recent approaches to obtain a good liberation of structural components in comminution, such as (semi)-autogenous grinding, surface grinding, blasting in water, microwave pretreatment, and electrical disintegration.
Waste acid and alkali solutions are discharged the most from printed circuit board, surface treatment and metalworking companies in the Banwol-Sihwa EIP, South Korea. However, most of companies are sold to consignment enterprises instead of self-recycling because they are composed of uncompetitive small companies, which then becomes the main cause of environmental pollutions and costs increase. This paper aims to evaluate economic value of recycled waste acid and alkali solutions by applying Life cycle cost (LCC) methodology. As a result, it proves that this recycling network has high and stable income potential. Furthermore, for exact economic evaluation, copper price trend prediction was evaluated by correlation and regression analysis about copper price variability of the most sensitive factor coming up with sensitivity analysis.
Titanium and its alloys have been used in bone plates/screws; these are designed to be removed after recovery. However, bone can sometimes bond to surface of implanted materials that remain in the body for long periods of time. This can lead to re-fracture of newly repaired bone during operations to remove the implants. The purpose of the present study was to synthesize bioinert films, including ZrO2 on pure Ti surfaces and to investigate hydroxyapatite (HAp) formation on the synthesized films in simulated body fluid (SBF). Pure Ti disks were chemically treated with H2O2/HNO3 aqueous solutions at 353 K for 20 min. The disks were hydrothermally treated with ZrOCl2/NH3/C6H8O7 (citric acid) aqueous solutions at 453 K for 12 h. The specimens were immersed in SBF, which was maintained at 310 K. After being soaked for different periods of time, the surfaces were observed by SEM. In the hydrothermal treatment with ZrOCl2/NH3 aqueous solution, the surface product was anatase-type TiO2. On the other hand, when citric acid was added the surface of Ti was covered homogeneously with a TiO2-ZrO2 composite film. This surface suppressed the precipitation of HAp during SBF soaking.
Porous titanium is an excellent biomaterial candidate because of its ability to maintain appropriate strength once it is implanted. The osteointegration of titanium and its alloys is less than that of bioactive ceramics. Therefore, various surface modification techniques have been developed to improve the osteointegration. We successfully prepared titanium dioxide (TiO2) and calcium titanate (CaTiO3) films on the surfaces of pure Ti by combined chemical-hydrothermal treatment. Especially in CaTiO3, the formation of apatite was promoted due to the release of Ca2+ from the surface of CaTiO3 in Hanks’ solution. Calcite (CaCO3) is a biodegradable material that must enhance hydroxyapatite (HAp) formation in simulated body fluid as well as in CaTiO3. The purpose of the present study was to synthesize bioactive films including CaCO3 on pure Ti substrates and porous titanium by chemical-hydrothermal treatment using Ca(OH)2 and KHCO3. The modified porous materials were tested mechanically in a compression test. CaTiO3-CaCO3 and TiO2-CaCO3 films were synthesized by choosing an ion concentration ratio of CO32-/Ca2+ in the aqueous solution for hydrothermal treatment. CaTiO3-CaCO3 films were also synthesized on porous titanium by hydrothermal treatment. Compressive properties of porous titanium after the treatment were similar to those prior to the treatment. The films produced by the present surface modification showed no significant changes compared to the original properties.
Recycling of printed circuit boards (PCBs) is an important subject not only from the treatment of waste but also from the recovery of valuable materials including rare metals. We have tried a special and selective grinding such as parts detachment from the board using drum typed agitation mill to concentrate a part of “rare metals”. The objective of this study is revealing the mechanism of parts detachment process from PCBs. A simulant PCBs on which nine capacitors were solder-mounted were used for the communition test using the agitation mill. Effects of rotation speed and the number of boards for parts detachment or board breakage were investigated. Both of parts detachment rate and board breakage rate were increased as rotation speed increased. On the other hand, as the number of boards increased, parts detachment rate was increased while board breakage rate was slightly increased. DEM simulation with and without particle breakage model was conducted. DEM simulation with spherical particle model (without particle breakage model) showed that board breakage was strongly affected by collision of PCBs to the wall in the normal direction while parts detachment was affected by both of collision of PCBs to the wall in the tangential direction and interaction between PCBs. To investigate the mechanism of parts detachment process more directly, DEM simulation with particle breakage model was also conducted. Simulation results obtained from DEM with particle breakage model corresponded to these experimental trends successfully.
In this study, calcium-doped silica was prepared by modifying sodium silicate-based silica gel in an aqueous solution of Ca(OH)2. Silica gels with less than 1 mm in size with different pH values were treated in Ca(OH)2 solution at concentrations ranging from 2 to 20 g/L and aged at 25, 60, and 90°C for 40 min. The BET surface area of the silica gel decreased while its pore size increased considerably after modification in Ca(OH)2 solution. The pH of 5% calcium-doped silica in water ranged from about 8.5 to 10, depending on the pH of silica gel, the aging temperature, and the concentration of the Ca(OH)2. When the concentration of the Ca(OH)2 solution was 20%, needle-like crystals of calcium silicate hydrate formed over the surface of silica gel.
Atmospheric scorodite synthesis reaction was developed. The reaction is oxidation of ferrous ion by oxygen gas in the presence of pentavalent arsenic ion, and synthesized scorodite is well-crystallized in a short retention time of 1 to 7 h. The resulting scorodite particles are as large as 15 μm, with less than 10% in moisture content, and they are readily washed and feature excellent packing properties. This scorodite synthesis process can be incorporated in hydrometallurgy process. The early stage of a mechanism scorodite synthesized in a novel atmospheric process was investigated. Crystalline scorodite was prepared even within 10 min in our novel process. We checked how to build up scorodite crystal by XRD, SEM and TEM. Then at very early stage, string type precipitates were found and after few hours it became plates and octahedron bodies. Environmental leach tests were also performed according to various countries’ batch leaching procedures. The comparisons were made among Japanese, U.S., Canadian, and Dutch leaching tests. In the United States Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure (TCLP) test (method 1311), the obtained scorodite particles released a very low, almost negligible concentration of arsenic in the pH range of 3 to 5, suggesting its long-term stability. In the leach tests of various pH solutions, it was shown that the scorodite solubility was turned greatly by outside environmental factors such as pH rather than long-term stability. In addition, the results showed scorodite released a considerably high concentration of arsenic under specific leaching conditions.