Kyoungkeun Yoo

The ammonia leaching of alloy produced from waste printed circuit boards smelting 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 kmol m− 3. The content of Cu could increase to 98% under the leaching conditions: 2 kmol m− 3 NH4Cl and 5 kmol m− 3 NH3 solution with 0.1 kmol m− 3 CuCl2 at 200 rpm and 30°C with 1% pulp density.

The effects of temperature and agitation speed on the leaching behaviors of tin and bismuth from spent lead free solder in nitric acid leach solution

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 effect of temperature on the leaching of monazite obtained from heavy mineral sands

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.

Treatment efficiency of acid mine drainage by the Ho-Nam Coal Mine passive treatment system

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.

Leaching behavior of valuable metals from by-product generated during purification of zinc electrolyte

Abstract 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.

Analysis of chemical forms of heavy metals in contaminated soil by sequential extraction methods

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 Tessiers 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.

Demagnetization followed by remagnetization of waste NdFeB magnet for reuse

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 Removal of Arsenic Ion in Electro-Coagulation Cell

ABSTRACT 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.

Interaction of Sb(III) with iron sulfide under anoxic conditions: Similarities and differences compared to As(III) interactions

This study examined the reaction mechanism of arsenite, As(III), and antimonite, Sb(III), with iron sulfide and compared their pH-dependent reaction behaviors under strictly anoxic environments. The comparison of Sb(III) with As(III), based on their chemical similarity, may provide useful insight into understanding the geochemical behavior of the less studied Sb(III). The pH-dependent batch sorption studies revealed that As(III) and Sb(III) displayed similar removal trends with pH in terms of the removal efficiency. However, the aqueous As(III) species transformed to thioarsenite species, while aqueous Sb(III) species remained inert under the highly sulfidic anoxic system. An X-ray absorption spectroscopy study demonstrated the reaction of As(III) and Sb(III) at acidic pH was closely related to the precipitation of sulfide minerals As2S3 and Sb2S3, respectively, as a consequence of the reaction with sulfide produced through mackinawite dissolution. Meanwhile, the removal at basic pH was inferred as a surface reaction, possibly through surface complexation, surface-precipitation, or both. In this study, the pH-dependent Sb(III) uptake mechanisms proved to be similar to the corresponding mechanisms for As(III) uptake, with mackinawite demonstrating a superior capacity to scavenge Sb(III) in ferrous and sulfide-rich reducing environments.

The removal of unburned carbon from fly ash by kerosene extraction

Abstract 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.