Search

Removal of cadmium and zinc ions from diluted solutions of their sulfate solutions with manganese dioxide, produced by ozone oxidation-precipitation reaction (OMD) under different conditions, has been investigated paying particular attention to correlation between the ion-uptake and the water content of OMD. Uptake of Cd2+ which is demonstrated to be an ion exchange reaction increases with an increase in the water content of OMD. The adsorbed water, which is liberated at lower temperature up to 200 °C, as well as the structural water of MnO2 takes part in the ion exchange reaction. One of the most outstanding features of OMD over both electrolytic MnO2 and chemically precipitated one is that OMD has a higher water content and shows fairly stronger ion exchanger nature than the other types of MnO2. For removal of Cd2+ with a reduced amount of Cd-contaminated MnO 2 residues, a two-stage treatment is considered to be effective. The first stage is addition of OMD in a small excess with respect to Cd2+ to uptake this ion at high efficiency and the second stage is addition of a small amount of OMD to make a high OMD / Cd2+ mole ratio to capture the remaining Cd2+ down to an adequately low concentration. Zinc ion was observed to be removed from its dilute solution by OMD addition in a similar manner to cadmium ion.

Recovery of Samarium and Neodymium from rare earth magnet scraps which contain-30% of Sm or Nd and 50-60% of Co or Fe was examined by the fractional crystallization of their sulfates. The results are summarized as follows: 1) When H2SO4was added into the nitric acid solution containing Sm and Co, the solubility of Sm decreased and Sm sulfate hydrate preferentially crystallized. 2) Samarium sulfate hydrate of 96.5% purity with recovery rate 87.1% was obtained from Sm Co5magnet scrap by the fractional crystallization. Effective results were also obtained when Sm2 (Co, Fe, Cu, Zr) 17 was examined similarly. 3) The addition of ethanol into the sulfuric acid-nitric acid solution containing Nd and Fe was proved to be effective for the decrease of solubility and fractional crystallization of Nd. 4) Neodymium sulfate hydrate of 96.8% purity with recovery rate 97.1% was obtained from Nd-Fe-B magnet scrap by the fractional crystallization of metal sulfates with addition of ethanol as well as H2S04.

An application of the alkaline hydrothermal process to the extraction of rare earth elements from complex ores was studied. A typical rare earth ore, bastnaesite, was reacted with NaOH solution under a high temperature and pressure to produce a mixture of rare earth hydroxides. The recovery of rare earth elements was measured as a function of temperature (373-723K) and NaOH concentration (1-5 mol/l). The results obtained were as follows;1. The optimum conditions for this process were 523-573K and 4-5 mol/l NaOH.2. Fluorine and silica in the are where extracted into the alkaline solution.3. The recovery of rare earth was decreased when the temperature exceeded 573K, which was assumed to be caused by the formation of cerium and praseodymium oxides.

Iron is no doubt the most fundamental element to materialize the human society. Present production of iron and steel is about 800 million t in the world and about 100 million t, including 7 million t of cast iron, in Japan. Regarding to recycling, 30% of crude steel is produced utilizing scrap as a secondary sourse of iron. Since the accumulation of the steel in Japan is becoming 1 billion t, the amount of scrap iron will become much larger in the future. Thus, effective smelting and steel making technologies with converter or energy saving electric furnace should be applied to the scrap. On the other hand, the quality of scrap in terms of chemical composition is becoming poorer as the products being needed light and small-sized and having lots of value added. Then the application of precise physical separation becomes important, as well as the development of technological and political system from the view point of the facility of recycling.

In the development of a continuous decomposition process of rare earth ores, the decompositionrate of bastonaesite by the alkaline hydro-thermal reaction was measured at 373-723K. The reaction was described by the dissolving core model. The apparent reaction rate constant, k', was proportional to the 3.9 power of NaOH concentration, which is given by the following equation.k'=2.79×107·exp(-1.41×104/T)·C3.9NaOH