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Electrowinning process to regenerate Sn4+from Sn2+in HCl solution using an electrowinning cell with anion exchange membrane was proposed to suggest a novel recycling process to recover Sn. During the tests, the effects of initial Sn2+concentration on the regeneration of Sn4+were investigated under the following condition; 7,000 mg/L, 10,000 mg/L, and 13,000 mg/L of Sn2+, 1 M HCl, 250 A/m2of current density, graphite anode, titanium cathode, room temperature, and 2 h. Electro-deposited Sn on the cathode showed dendritic structure regardless of the Sn2+concentration and no change of Sn concentration was observed in the anolyte. Leaching tests were performed using the anolyte, obtained from the electrowinning tests, to examine the amount of regenerated Sn4+concentration during electrowinning process. Based on the results of Sn leaching tests, it was found that 84.44%, 81.03%, and 79.43% of Sn4+were regenerated from 7,000 mg/L, 10,000 mg/L, 13,000 mg/L initial concentration of Sn2+solution, respectively. Consequently, it was found that the regeneration of Sn4+can occur during the electrowinning process at the same time with Sn recovery and Sn4+can be reused as an oxidant to leach Sn successfully.

The recycling process was developed to remove and recover unburned carbon from fly ash using kerosene extraction. The effects of experimental factors such as shaking time, initial unburned carbon content, and organic to suspension (O/S) ratio on the removal of unburned carbon were investigated to obtain the optimum conditions. The results indicate that the removal ratio of unburned carbon increased with increasing shaking times and decreasing the initial unburned carbon content, but the residual amount of unburned carbon was independent of O/S ratio. The content of unburned carbon decreased successfully to less than 3% under the following conditions; 15 min in shaking time, 10% in pulp density, 30 °C in temperature, 200 rpm in shaking speed, and 0.5 in O/S ratio.

Purification cake generated during cementation process contains valuable and hazardous metals such as cadmium, copper, zinc, lead, cobalt, nickel, and antimony. The purification cake has been dumped in landfill sites, and this could cause the environmental problem such as leak of leachate and the loss of valuable metal. The present study is aimed at investigating the leaching behaviors of metals in sulfuric acid solution to recover the valuable metals. The effects of reaction time, temperature, sulfuric acid concentration, agitation speed, pulp density were investigated to establish the leaching conditions. More than 99.9% of cadmium and zinc were leached within 5 min and same ratio of cobalt was leached within 30 min. Copper, nickel, and antimony were leached 99, 97, 95%, respectively, after 60 min. Lead was detected about 2% in 60 min in 1.0 M sulfuric acid at 50 °C and 400 rpm with 10 g/L pulp density for 180 min. It is possible that lead remains as a precipitate and cadmium, zinc, copper, cobalt, nickel, antimony in leach solution are recovered.

The effect of grinding time on the particle size distribution and chemical composition of manganese nodule was investigated to provide information such as the density and the metal contents of Mn, Fe, Ni, and Co for efficient design of separation process on ship. Therefore, the manganese nodules obtained from Pacific Ocean were ground with the mortar and ball mill, and then the density and the contents of metals were measured with particle size. In the mortar grinding test, the density and Mn contents of the ground product increased as the particle size increased indicating that the smaller particle contains less metallic components. In the ball milling test, the weight distribution of particle with less than 150 µm increased from 2.6 to 18.8% with the grinding time from 20 to 180 min, respectively. In the particle range with – 150 µm, the contents of Mn and Ni increased with increasing grinding time, whereas there is a little difference in the Fe and Co contents with the grinding time. The increase in density with grinding time resulted from the increase in the contents of Mn. These kinds of information are useful to design the efficient separation process on ships.

Nitric acid leaching was performed to separate tin and bismuth in spent Pb-free solder. The effects of agitation speed and leaching temperatures on the leaching behaviors of tin and bismuth were investigated to recover tin and bismuth from the spent solder, respectively. The leaching efficiency of bismuth increased rapidly with increasing agitation speeds and temperatures, and the efficiency is found to be 97.8% under the following leaching conditions: nitric acid concentration of 1 k mol m- 3, agitation speed of 400 rpm, 1% pulp density, leaching temperature of 90°C, leaching time of 1 hour. In the case of tin, the leaching efficiency increased and then decreased during leaching tests, and a white precipitate was observed in the reactor. XRD results indicate that tin precipitated as stannic acid (SnO2 H2O). Consequently, bismuth and tin could be separated successfully by nitric acid leaching process.

The ammonia leaching tests were carried out to recover valuable metals from alloy obtained from smelting reduction process of mobile phone printed circuit boards. Leaching factors such as kinds of salt, ammonia concentration, and the interaction of metals, which are components of PCB, were investigated to improve the leaching efficiency. In the leaching tests using metal powders such as Zn, Sn, Ni, and Pb to investigate the interaction of metals, zinc was easily dissolved in ammonia solution, whereas Sn and Ni were not detected or the Pb concentration decreased rapidly. The metal concentrations increased with an increase in NH3 concentration from 1 to 5 kmolm-33. The content of Cu could increase to 98% under the leaching conditions: 2 kmolm-3 NH4Cl and 5 kmolm-3 NH3 solution with 0.1 kmolm-3 CuCl2 at 200 rpm and 30°C with 1% pulp density.

The samples collected from soils and sediments near the mouth of a river (samples A, B, and C), port (sample D), or shooting range (samples E and F) were investigated with Tessier's sequential extraction method to design the remediation process for contaminated sites. This method was chosen to determine the chemical forms of heavy metal contaminants, which consists of five fractions such as 'exchangeable', 'bound to carbonate', 'bound to oxide', 'bound to organic matter', and 'residue'. In the case of samples from sediments near the mouth of a river, zinc (Zn) distributes in the fractions 'bound to oxide' and 'bound to organic matter', while copper is observed in the fractions 'bound to organic matter' and 'residue', respectively. When the sample obtained from the sediment near a port was examined, most of Zn distributes in the fractions 'bound to organic matter' and 'residue'. In sites E and F, lead, Zn, and copper distributed in the fractions 'bound to carbonate' and 'bound to oxide'. On the basis of results, physical treatment followed by chemical leaching for sites A, B, and C, physical separation process for site D, and chemical treatment process for sites E and F would be required to remediate the contaminated sites.

New recycling process was proposed to reuse the waste NdFeB magnet scrap powder from the manufacturing process of NdFeB magnet and disc from motor of waste washing machine. The feasibility study was carried out to examine demagnetizing followed by remagnetizing the waste NdFeB magnets. The X-ray diffractometer patterns showed that the peaks of Fe were observed and those of NdFeB disappeared with increasing temperature to more than 500°C under the Ar atmosphere. The weight increased more under the air atmosphere than under the Ar atmosphere in TG-DTA test. After the waste NdFeB magnets were demagnetized at 300-500°C under the air and Ar atmospheres, they were remagnetized, and the magnetic power was measured. All remagnetization ratios showed more than 100% except the waste NdFeB magnet demagnetized at 500°C under the air atmosphere. The remagnetization ratio decreased with increasing the demagnetization temperature, and the decrease is faster under the air atmosphere than under the Ar atmosphere, which would result from the metal crystal structure change.

The Ho-nam coal mine passive treatment system, which consists of an oxidation pond, successive alkalinity producing system (SAPS) and aerobic wetland, was investigated to estimate the treatment efficiency of the entire system and each treatment step. After the acid mine drainage of Ho-nam coal mine moves through the entire system, metal concentration and acidity decreases and alkalinity increases. Acid mine drainage has been treated successfully by the Ho-nam coal mine passive treatment system. However, iron ions were not removed sufficiently in the oxidation pond even though ferrous ions oxidized to ferric ions. Furthermore, in SAPS, Fe concentration decreased rapidly but sulfate reducing bacteria activity was not shown in the system. These results suggest that the objectives of each step were not achieved as designed, although the system was found to be successful.

Pressure leaching, electrogenerated chlorine leaching and concentrated sulfuric acid leaching were performed to investigate the leaching behavior of monazite concentrate with various temperature ranges. The pressure leaching was tested at 5 atm and 220°C and the concentrations of Ce and La increase with increasing sulfuric acid concentration from 0.01 mol/L to 1 mol/L and decreasing the particle size of monazite concentrate from -200 mesh - + 325 mesh to -325 mesh. In the electrogenerated chlorine leaching system, the concentration of La decreases with increasing temperature from 30°C to 70°C, which resulted from a decrease in solubility of chlorine with increasing temperature. In the concentrated sulfuric acid leaching system, the leaching ratios of La and Nd increase to over 99% with increasing temperature to 220°C. The higher metal concentration of Ce, La and Nd are obtained in the concentrated sulfuric acid leaching system than in the pressure leaching and the electrogenerated chlorine leaching system. This result suggests that higher temperature and concentration of sulfuric acid could accelerate the dissolution of monazite concentrate.

Copper and iron ions were removed by an adsorption process with waste seaweeds, and the adsorption behavior of Cu and Fe ions was investigated by the Freundlich and Langmuir isotherm equations. The removal ratios of Cu were found to be from 87.1 % to 91.8 %, whereas those of Fe were from 17.0 % to 72.1 %. When the Freundlich and Langmuir isotherms were plotted using the Cu and Fe adsorption results, the isotherm plots for Cu showed good correlation coefficients, but the coefficients of Fe were low due to low removal ratio. In the adsorption tests using the mixture solution with Cu and Fe ion, the removal ratio of Cu ion is much lower in the mixture solution than in the Cu solution, whereas that of Fe shows the similar removal ratios in both solutions. These results suggest that the adsorption of Cu onto the waste seaweed could be hindered by the competitive adsorption of Fe ion. © 2011 Taylor & Francis Group, LLC.

An arsenic leaching test was performed to extract arsenic contaminant from tailing sediment under basic condition with NaHS. The effects of particle size, NaHS concentration, temperature, and agitation speed were investigated to determine optimum leaching condition for the removal of arsenic from the tailing sediment. The leaching rate increases with decreasing the particle sizes of enargite and tailing sediment, which would result from the fact that arsenic distributes uniformly in the enargite and tailing sediment particle. The addition of NaHS accelerated the arsenic leaching rate, and this result suggests that some of arsenic in the tailing would exist as enargite or be bound to enargite. The arsenic leaching rates increased with increasing temperature and agitation speed. The arsenic leaching rates of enargite and tailing sediment were found to be 87% and 63%, respectively, under the conditions; particle size, -75 µm; temperature, 80°C; NaHS concentration, 1.5 kmol m -3 ; NaOH concentration, 1.1 kmol m -3 ; agitation speed, 400 rpm; pulp density, 5 kg m -3 (enargite) and 25 kg m -3 (tailing sediment). © 2011 Taylor & Francis Group, LLC.

The removal of As(V) and As(III) was investigated using electro-coagulation (EC) cell. Adsorption on hydro ferric oxide (HFO) generated by EC cell shows high ratio at lower pH and decreases with increasing pH. The removal efficiencies are higher in the feed solution with As(III) than with As(V). Total arsenic removal ratio is higher in the feed solution with As(III) than with As(V). Total arsenic removal ratios in EC process are over 90% at pH 4 to 9 at 1.0 A in the feed solution with As(III). At 0.5 A, As(III) adsorption ratio is 36.84% at pH 4 and total arsenic removal ratio is 60.79%, and As(III) adsorption ratio is 88.19% at pH 4 and total arsenic removal ratio is 91.13% at 1.0 A. High adsorption ratio of As(V) increases total arsenic removal ratio. In the EC cell, As(III) species could be oxidized to As(V) species, and high arsenic removal ratio is expected at low pH range by using EC process. The oxidation ratios of As(III) to As(V) are 7.1 to 41.3% and 11.1 to 27.7% at 0.5 A and 1.0 A, respectively. The EC process can oxidize As(III) to As(V), and As(V) has more affinity on HFO surface than As(III) at low pH ranges. This result suggest that this technology could be used to remove As ion from acid mine drainage. © 2011 Taylor & Francis Group, LLC.