Fumio Saito

A mechanochemical method was used to treat a used evaporation tape, aiming at recovering the contained cobalt (Co) metal and achieving dechlorination non-thermally by dry grinding the tape only or cogrinding with calcium oxide (CaO), respectively. The induced mechanochemical reaction between Co and chlorine in the tape leads to the formation of cobalt chloride, which is water-soluble, offering a novel process to recover the metal from the tape. On the other hand, cogrinding with CaO allows the complete transformation of chlorine in the tape into water-soluble inorganic chloride. The mechanochemical dechlorination process was characterized by an XRD analysis, TG-DTA analysis, SEM photography, Raman analysis and quantitative measurement of the soluble compositions.

Co-grinding nonferrous metal oxides and sulphur together with iron/aluminium metal stimulates a solid-state reaction to form the nonferrous metal sulphides and iron/aluminium oxide, allowing the use of the current mineral processing technologies to recover metals from various kinds of wastes.

Aluminum hydroxide (gibbsite) powder was ground in air by a double rotating cylinders mill (UF mill) under two different grinding conditions: one is grinding by rotating both cylinders inversely, called Case-1, and the other grinding by rotating the inner cylinder only, called Case-2. The ground powder was mixed together with cement powders with water to form a hardened body to investigate the effect of grinding on hardened body properties. The impact energy density of balls in Case-1 is higher than that in Case-2. The reactivity of product ground in Case-1 is lower than that in Case-2, when they are compared at the same degree of amorphization for the gibbsite sample. This leads to the formation of calcium aluminate hydrate with dense phase in the hardened body prepared in the Case-1. The compressive strength of hardened body prepared in Case-1 is higher than that in Case-2. The grinding gibbsite sample in Case-1 is suitable for the product to form the hardened body with a high compressive strength.

Fluorescent powder was subjected to mechanochemical (MC) treatment using a planetary mill to control its structural change followed by selective leaching of Y and Eu with 1N HCl solution at room temperature. The crystal structure of the fluorescent powder tends to be transferred into disordered state by the MC treatment. It is possible to control the crystal disordered state by choosing the MC condition such as media size and rotational speed of the mill. The optimum condition gives us to improve the yield of Y and Eu, depressing the yield of La, Ce and Tb in the acid leaching. In the present experiment using 15 mm ball size, the preferable MC treatment would be conducted within about 20 minutes at 400rpm in mill rotational speed.

Mixed grinding of the two sets of starting materials was conducted under atmospheric dry condition by a planetary ball mill to investigate the formation of forsterite in the sintered body. These were talc-magnesium carbonate basic (MCB) and talc-magnesium oxide powder mixtures. The specific surface area of the ground product increases in the initial stage, subsequently it decreases due to aggregation of the obtained fine particles. The grinding the mixture of talc and (MCB) causes structural change into amorphization, while crystalline phases still remain in the ground mixture of talc and MgO. This amorphization in the former mixture resuls in the formation of forsterite single phase at lower temperature than that of the unground one as well as that of the latter one. The addition of methanol and regrinding of the mixture induce lowering of sintering temperature by about 100 K in the formation of forsterite single phase.

Mechanochemical solid-phase reactions for hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) from different kinds of constituent powder mixture were investigated. HAp monophase can be produced from the three sets of powder mixtures of Ca(H₂PO₄)₂H₂O-CaO, Ca(H₂PO₄)₂H₂O-Ca(OH)₂, and Ca(H₂PO₄)₂H₂O-CaCO₃ (Ca/P atomic ratio: 1.67) by dry grinding using a planetary ball mill at room temperature. All the solid-phase reactions for HAp from the starting mixtures were almost completed within 60 min of grinding. Among them, Ca(H₂PO₄)₂H₂O-Ca(OH)₂ mixture is the most suitable one for the preparation of HAp. The amount of free H₂O released during mechanochemical treatment plays a key role in these synthesis reactions. The formation of HAp is improved as grinding progresses. The completion of synthesis reactions is confirmed by measuring the equilibrium pH of powder suspensions of ground mixtures.

A novel process for synthesizing zeolite-A and X from kaolinite activated by dry grinding is investigated. The process consists of grinding of kaolinite and subsequent reaction with NaOH solution at 60°C. Zeolite-A and X can be synthesized from the process under normal pressure. Crystallization of zeolite-A and X is influenced by the activated state of kaolinite, and the formation of zeolite-X is accelerated as the activated state of kaolinite is improved. Wet milling of activated kaolinite in NaOH solution promotes formation of zeolite-X, of which specific surface area becomes extremely large.

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A powder mixture of calcium oxide (CaO) and silica-gel (amorphous SiO2) was subjected to grinding under dry atmospheric condition using a planetary ball mill to investigate its effect on synthesis of para-wollastonite (CaO·SiO2) powder by heating. The grinding of the mixture changes a crystalline structure of CaO into amorphous one within 5 hours. Accordingly, the mixture ground for 5 hours aggregates with homogeneous chemical composition, leading to the formation of a precursor of para-wollastonite by heating at 923 K. Para-wollastonite can be synthesized by heating the mixture ground for 2 hours at 1,273 K for 2 hours, while heating at around 1,400 K for about one week is necessary to synthesize it from the original mixture.