Shuji Owada

Sorption mechanisms of arsenate during coprecipitation with ferrihydrite in aqueous solution.

Dilute arsenate (As(V)) coprecipitation by ferrihydrite was investigated to determine if treatment of acid mine drainage containing dilute As(V) using coprecipitation is feasible. The sorption density obtained at pH 5 and 7 was nearly identical when As(V) was coprecipitated with ferrihydrite, while it was higher at pH 5 when As(V) was adsorbed on the ferrihydrite. The high sorption density of As(V) to ferrihydrite in coprecipitation with 1-h reaction time suggested that coprecipitation occurs via both adsorption and precipitation. Furthermore, the relationship between residual As(V) and sorption density revealed a BET-type isotherm, with a transition point from a low residual As(V) concentration to a high residual As(V) concentration being observed for all initial As(V) concentrations between 0.15 and 0.44 mmol/dm(3) when the initial molar ratio was 0.56 at pH 5 and 7. X-ray diffraction and the zeta potential revealed that the transition point from surface complexation to precipitation was obtained when the initial As/Fe ratio was 0.4 or 0.5. When dilute As(V) was coprecipitated with ferrihydrite at pH 5 and 7, it was primarily adsorbed as a surface complex when the initial molar ratio was As/Fe < 0.4, while a ferric arsenate and surface complex was formed when this ratio was >or= 0.4.

Development of a centrifugal mill - A chain of simulation, equipment design and model validation

Abstract A centrifugal mill was designed after a wide range of information obtained from the analysis on the mill model developed by the discrete element method. The simulation model is capable of predicting the ball motion, energy spectrum, map of energy dissipation in the mill body, etc., reconstructed from individual ball-to-ball and ball-to-wall interactions. Grinding tests conducted on the centrifugal mill developed were found to reproduce reasonably well the characteristics of the mill predicted by the simulation model. Since the simulation does not deal directly with the comminution performance itself, the major mission of the test work on the actual mill was to verify and to supplement the information acquired by simulation.

Mineralogical properties and fundamental mineral processing behaviour of the chromite contained in laterite leach residue

Abstract In order to utilize chromite in the laterite residue discharged from the large-scale Ni-leaching plant in the Philippines, its state of distribution, mineralogical properties, grindability, floatability, and magnetism were investigated. Chromite particles are concentrated over a 37μm size range, and poor in liberation. There are three different groups of chromite (A, B, and C), categorized according to their polished section, chemical composition, lattice constant, and specific gravity. Some of these differences affect the mineral processing behavior to a considerable degree. The grindability of chromite in leach residue is relatively high compared with that of chromites from other regions. Flotation is controlled by interfacial electrical attraction when ionic collectors are used, and the flotation peak appears in the vicinity of the PZC when NaOl is used. The order of floatability among the three groups of chromite particles is A>B>C, which indicates that a difference in surface structure by group affects floatability. Chromite from leach residue reveals paramagnetism at room temperature. The higher the solid solubility of magnetic ions (Fe 2+ , Cr 3+ , and Fe 3+ ), the greater the susceptibility is. In other words, the susceptibilities among the three groups are in the order of C>A>B.

Electromagnetic Field Analysis on the Behavior of Selective Breakage at Phase Boundary in Electrical Disintegration

It is important in the comminution stage of waste treatment to liberate objective components from others for achieving the following compositional separation. However traditional (mechanical) comminution methods usually have problems of low selectivity of the breakage of phase boundary and low energy efficiency.

Application of physical separation technologies to the shredder fluffs

The compositional structure of the two kinds of shredder fluffs generated from scrap automobiles and electrical home appliances were compared with each other on material and elemental compositions and liberation state. It was found that compositional elements were classified into three kinds of groups of different size and that valuable elements were concentrated in larger size and toxic ones in smaller size ranges. The combination of physical separation methods, jigging, magnetic, eddy current and electrostatic separations was able to produce metal concentrates of Fe, Cu and Al suitable for smelter feeds with relatively high recoveries and contents. Plastic and wooden materials suitable for energy recovery were also produced in the float or sink and float separation.

Novel Pretreatment Process of Critical Metals Bearing E-Scrap By Using Electric Pulse Disintegration

Recovering various metals, involving minor rare metals, from electronic devices is important for conserving resources and establishing a sustainable society. This paper describes an economically feasible and radical process for such recovery, especially, for Ta concentration from printed circuit boards (PCBs) which is the two-stage electric pulse disintegration (ED) process. Ta capacitors are detached from the PCBs in the first stage, and the sintered Ta contained within the capacitors is liberated from the capacitor in the second stage. It has been indicated that as much as 100% of Ta capacitors was detached from PCBs in nondestructive form in the first stage of ED and that 95% of sintered Ta and MnO2 phases was liberated from covered plastics, which is much higher than the 46% detachment achieved when using mechanical roll crusher. The detailed detachment and liberation mechanisms of both stages were also described, and an upper limit of the solution’s conductivity in the second-stage ED was indicated.