Leaching studies for tin recovery from waste e-scrap

Printed circuit boards (PCBs) are the most essential components of all electrical and electronic equipments, which contain noteworthy quantity of metals, some of which are toxic to life and all of which are valuable resources. Therefore, recycling of PCBs is necessary for the safe disposal/utilization of these metals. Present paper is a part of developing Indo-Korean recycling technique consists of organic swelling pre-treatment technique for the liberation of thin layer of metallic sheet and the treatment of epoxy resin to remove/recover toxic soldering material. To optimize the parameters required for recovery of tin from waste PCBs, initially the bench scale studies were carried out using fresh solder (containing 52.6% Sn and 47.3% Pb) varying the acid concentration, temperature, mixing time and pulp density. The experimental data indicate that 95.79% of tin was leached out from solder material using 5.5M HCl at fixed pulp density 50g/L and temperature 90°C in mixing time 165min. Kinetic studies followed the chemical reaction controlled dense constant size cylindrical particles with activation energy of 117.68kJ/mol. However, 97.79% of tin was found to be leached out from solder materials of liberated swelled epoxy resin using 4.5M HCl at 90°C, mixing time 60min and pulp density 50g/L. From the leach liquor of solder materials of epoxy resin, the precipitate of sodium stannate as value added product was obtained at pH 1.9. The Pb from the leach residue was removed by using 0.1M nitric acid at 90°C in mixing time 45min and pulp density 10g/L. The metal free epoxy resin could be disposed-of safely/used as filling material without affecting the environment.     

Study on integrated management of PCB containing waste and PCB contaminated waste: proposal of new congeners for quantification

In the present study, new congeners were selected for the efficient management of PCB containing waste and PCB contaminated waste, and the applicability of these new indicators was confirmed. As a result, 8 indicator congeners and 4 index peaks which were named “Proposed new method 1” and “Proposed new method 2” were selected. For the assessment of a novel quantitative method, comparative tests using conventional methods were conducted, and the factors for total PCB were calculated for each method. Results from these tests showed that the average values for the factors of CEN/TC19/WG22, DIN 51527, and the test method by the disposal regulation for ocean dumping in Korea were 1.86, 3.47, and 2.52, respectively, while those for the proposed new method 1 and proposed new method 2 were 2.98 and 5.56, respectively. For PCB contaminated waste, the factor was found to be 1.99, 3.42, and 3.02 using the conventional methods, 2.67 using the proposed new method 1, and 5.57 using the proposed new method 2. It is expected that, in accordance with the results of the present study, the management of PCB waste can be integrated, regardless of the type of waste involved.     

Synchronization of amniotic fluid cells for high resolution cytogenetics

A high resolution technique was applied to amniotic fluid cells by synchronization. After inoculation, the cells were incubated for 30 h in the presence of either thymidine or 5-bromodeoxyuridine (BrdU). After removal of the blocking agent and addition of a low concentration of thymidine, the cells were incubated for another 6 1/2–7 h, then harvested in prometaphase without colcemid. This technique gives a mitotic index of 3·7 per cent after thymidine synchronization and of 3·2 per cent after BrdU synchronization, and more than half of the mitoses were in the earlier phases with the chromosomes showing more than 550 bands per haploid set. GBG, GTG, and RHG prometaphases are presented. Precise high-resolution banding of chromosomes of amniotic fluid cells can increase diagnostic accuracy.     

Catalytic wet oxidation of ammonia: why is N2 formed preferentially against NO3 -?

The role of catalyst and the reason for the preferential formation of N(2) in the catalytic oxidation reaction of ammonia in water over a Ru (3wt.%)/TiO(2) catalyst were elucidated. It was verified that the catalyst in the reaction had no direct relevance to the selective formation of N(2), but was responsible only for the oxidation of aqueous ammonia, NH(3)(aq), finally giving a molecule of nitrous acid. The preferential production of N(2) was experimentally demonstrated due to the homogeneous aqueous phase reaction of the nitrous acid-dissociated NO(2)(-) with NH(4)(+) ions. Even under the highly oxidizing condition, NO(2)(-) was much more likely to react with NH(4)(+) to form N(2) than being oxidized over the catalyst to NO(3)(-) as long as NH(4)(+) was available in solution.     

Utilization of coal fly ash as a slow-release granular medium for soil improvement

This work proposes a new potential application of waste coal fly ash as a K fertilizer support. Fly ash was reacted with KOH to facilitate the impregnation of K as well as to enhance the bonding force. In particular, the applied process resulted in a significant slow-releasing characteristic of fertilizer elements. To examine the effect of K impregnation, a few detailed leaching tests were carried out in terms of process variables such as reaction time and temperature, sintering time and temperature, and KOH concentration. The current experiment presented an optimum preparation condition that is competitive with conventional commercial fertilizers. The manufactured ash fertilizers inhibited release of the K elements. It was also found through the continuous leaching test with pure water that the ash fertilizer had excellent moisture absorbability. However, the effects of some trace elements in fly ash on soil health and crop productivity as well as environmental considerations need to be established with long-term studies.     

Filtration of fullerene and copper oxide nanoparticles using surface-modified microfilters

This study evaluated the filtration of engineered nanoparticles of fullerene and copper oxide (CuO) from water by using surface-modified microsized filters. The surfaces of microsized filters of cellulose acetate and glass fibers were coated with cationic and anionic surfactants to give them positively and negatively charged surfaces, respectively. Uncoated microfilters removed 30 % of a fullerene suspension, while no nanosized CuO suspension was removed. Cationic surfactant-coated filters enhanced the removal efficiency up to 70 % for the fullerene suspension, while the anionic surfactant-coated filters could not remove fullerene at all. The positively charged filters with cationic surfactant coating could easily adsorb negatively charged fullerenes on their surfaces. However, none of the surfactant-coated filters removed the CuO nanoparticles because the nanoparticles were not affected by the electrical charge of the filtration medium. The Hamaker constants of nanoparticles interacting with the filter materials in water were calculated to study these interactions. The Hamaker constant of fullerene interacting with cellulose acetate in water, 4.68E???21 J, was higher than that of interacting with quartz in water, 2.59E???21 J. However, the Hamaker constants of CuO interacting with quartz and cellulose acetate in water were both negative values, implying repulsive van der Waals interactions. The curves of potential energy of interaction between nanoparticles and the various filter media implied that the nanoparticles were very stable in water, and so, natural deposition of nanoparticles on the filters would not occur. Therefore, electrical bonding and hydrophobic interactions were the forces dominating fullerene removal by positively charged filters.     

Chemical characteristics of long-range transport aerosol at background sites in Korea

In this study, background concentration sites of Deokjeok and Gosan, which were deemed suitable for monitoring the impact of long-range transported air pollutants, were selected. An investigation of the source types of pollutants, their locations, and relative quantitative contributions to the particulate concentrations at both sites using appropriate methodologies to make initial estimations was conducted. Episodic measurements of PM_2.5, PM₁₀, and size distribution, along with its ion and carbon components were performed from 2005 to 2007, and a comprehensive analysis of the results was conducted utilizing back trajectory analysis. As for frequency of wind direction, it was quite apparent that the two sites are heavily influenced by air masses originating from the eastern and northern regions of China. For PM_2.5 and PM₁₀, the mass concentrations from north and east China were higher than other cases, originating from the ocean. In the northerly-wind case, meteorological properties for Deokjeok and Gosan and the influence of carbon emissions from northwest Korea resulted in a changing of air mass properties during transport. As was the case with mass concentration, the highest contribution for ionic and carbon components of PM_2.5 and PM₁₀ for both sites appeared for the westerly wind case. A specially high relative contribution, greater than 1.4 times, was apparent in the secondary aerosol case because of a large influence of long-range transported pollutants from east China. Carbon components exhibited different behaviors for the northerly and westerly wind cases compared with secondary aerosol. The major reason for this discrepancy appears to be the carbon emissions from northwest Korea.     

Assessment of Wastewater Reuse Effects on Nutrient Loads from Paddy Field Using Field-Scale Water Quality Model

CREAMS-PADDY, a modified version of the field-scale CREAMS model, simulates the hydrologic, sediment, and nutrient cycles in paddy fields. The CREAMS-PADDY model was applied to estimate the effects of using wastewater for irrigation on nutrient loads from paddy fields in Republic of Korea. The model was calibrated and validated using data from two rice paddy fields. The coefficient of determination between observed and simulated total nitrogen and total phosphorus were 0.92 and 0.57, respectively, for the calibration period and 0.84 and 0.73 for the validation period. Simulations showed that when using wastewater for irrigation, the total nitrogen loads increased by 210% and total phosphorus by 1,270% when compared with conventional water irrigation. The total nitrogen and total phosphorus concentration in the ponded water increased by 254 and 534%, respectively, when compared with conventional water irrigation. The effect of reducing N and P fertilizer application rates by 10, 30, and 50% on nutrient loads exiting a paddy field were also simulated using the validated CREAMS-PADDY model. These simulations indicated that total phosphorus loads from the paddy were reduced only slightly by reducing the fertilizer, while total nitrogen loads were reduced by as much as 8.8, 16.6, and 24.4% when N ferlitizer rates were reduced by 10, 30, and 50%, respectively. An erratum to this article can be found at