Soobin Yim

Copper leaching from brake wear debris in standard extraction solutionsElectronic supplementary information (ESI) available: thermodynamic equilibrium speciation results from the geochemical model MINTEQ. See http://www.rsc.org/suppdata/em/b3/b303820c/

Quantification of the copper content of and copper leaching from a disc brake wear debris sample was performed using microwave-assisted acid digestion, the Federal Toxicity Characteristic Leaching Procedure (TCLP), and the State of California Waste Extraction Test (WET). The brake wear debris tested was a composite sample obtained from a brake dynamometer test of one brake pad source material. Comparative digestion studies demonstrated that a modified aqua regia matrix (HNO3:HCl:H2O2 = 1:3:0.5) optimized the digestion effectiveness for determining the total copper content in the brake wear debris. No significant sample heterogeneity within the brake wear debris was observed, based on statistically indistinguishable total copper content results for subsamples with a wide range of sample masses. Upon pooling all subsample results, an overall total copper content for the composite brake wear debris sample was determined to be 10.8% (g/g), with a 95% confidence limit of +/- 0.5% (g/g). Copper leaching increased with decreasing solid-to-liquid ratios in TCLP tests, but was unaffected by the solid-to-liquid ratio in the WET. For a 1:10(4) (g/g) solid-to-liquid ratio, 85% and 99% of the total mass of copper present in the composite brake wear debris sample was leached into solution during the TCLP and WET, respectively. Rate studies also demonstrated that the WET resulted in a faster rate and higher extent of copper leaching relative to the TCLP. Compared to reference copper-containing materials, the composite brake wear debris sample exhibited relatively higher TCLP and WET copper leaching characteristics. The higher copper leaching exhibited by the brake wear debris sample may have resulted from its higher specific surface area and/or from changes in the chemical form of copper that occurred during the braking process.

Effects of organic ligands and pH on the leaching of copper from brake wear debris in model environmental solutions

Copper leaching from a disc brake wear debris sample was examined in a variety of aqueous solutions to simulate potential leaching processes during rain events and in surface waters. Synthetic rainwater leached 40% of the total copper present in the brake wear debris into solution after 18 h in batch reactors, which was approximately three times more copper than that extracted by the US Environmental Protection Agencys Synthetic Precipitation Leaching Procedure. Formate and acetate were responsible for the enhanced copper leaching, as demonstrated by higher average amounts of leached copper in synthetic rainwater with- versus without the organic acids (40 versus 31% recovery). This observation suggests leaching tests that do not incorporate the appropriate types and concentrations of organic ligands present in rainwater will likely underestimate copper mobilization from brake wear debris during rain events. Leaching of copper from the brake wear debris ranged from 23 to 40% in solutions containing 3 to 15 mg C L(-1) dissolved humic substances, and was higher still in solutions containing relatively high concentrations of the synthetic metal chelating agent ethylenediaminetetraacetic acid. Static pH tests demonstrated that copper leaching from brake wear debris is highly pH dependent, with more leaching occurring at lower solution pH values. Leaching rate studies revealed that equilibrium generally was not attained within 48 h in the model solutions, indicating that additional copper can be expected to be released in environments where brake wear debris is exposed to long-term leaching processes.

Optimization of nitrogen removal in a sequencing batch reactor system by variation of the time distribution

In this study, we investigated the variations of the nitrogen removal and mass balance of a sequencing batch reactor (SBR) system with the duration of the second anoxic period (the anoxic (II) period); durations of 0, 70, 100, and 130 minutes were tested in one cycle of SBR operation to determine the optimum conditions for the operation of the SBR and increase its nitrogen removal efficiency. The SBR system was operated under the conditions as follows: a sludge retention time (SRT) of 17.5 days, an operation time of 6 hours per cycle, a hydraulic retention time (HRT) of 12 hours, an influent COD loading of 0.4 kg/m3/day, and an influent nitrogen loading of 0.068 kgT-N/m3/day. For anoxic (II) phase duration times of 0, 70, 100, and 130 minutes, the amounts of nitrogen removed in the clarified water effluent for the synthetic wastewater were 73.1, 64.9, 59.0, and 49.3 mg/cycle, with nitrogen removal percentages of 59.7, 65.4, 68.8, and 73.8%, respectively. The amounts of nitrogen removed during the sludge waste process were 21.8, 22.0, 22.4, and 22.3 mg/cycle, respectively, indicating that the amount of nitrogen removed during the sludge waste process is not affected by changes in the time allotted to the anoxic (II) period. The amounts of nitrogen removed by denitrification were 76.5, 83.0, 90.5, and 96.5 mg/cycle, respectively indicating that increasing the duration of the anoxic (II) period increases the efficiency of nitrogen removal. The nitrogen mass balances were calculated as the percentages of nitrogen removed in the clarified water effluent or by denitrification and sludge waste processing in each cycle of SBR operation and were found to be excellent: 96.8%, 96.3%, 96.8%, and 95.2% for anoxic (II) phase durations of 0, 70, 100, and 130 minutes, respectively.

Phosphorus removal characteristics in hydroxyapatite crystallization using converter slag.

This study was performed to investigate the phosphorus removal characteristics in hydroxyapatite (HAP) crystallization using converter slag as a seed crystal and the usefulness of a slag column reactor system. The effects of alkalinity, and the isomorphic-substitutable presence of ionic magnesium, fluoride, and iron on HAP crystallization seeded with converter slag, were examined using a batch reactor system. The phosphorus removal efficiencies of the batch reactor system were found to increase with increases in the iron and fluoride ion concentrations, and to decrease with increases in the alkalinity and magnesium ion concentration. A column reactor system for HAP crystallization using converter slag was found to achieve high, stable levels of phosphorus elimination: the average PO4-P removal efficiency over 414 days of operation was 90.4%, in which the effluent phosphorus concentration was maintained at less than 0.5 mg/L under the appropriate phosphorus crystallization conditions. The X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra of the crystalline material deposited on the seed particles exhibited peaks consistent with HAP. Scanning electron micrograph (SEM) images showed that finely distributed crystalline material was formed on the surfaces of the seed particles. Energy dispersive X-ray spectroscopy (EDS) mapping analysis revealed that the molar Ca/P composition ratio of the crystalline material was 1.72.