Advanced Materials Research Vol. 878

Abstract: Due to shorter and shorter life span and the rapid development of flat panel display, plasma display panel (PDP) is now becoming a new kind of e-waste. In order to remove heavy metals, such as As, Ba, Cu, Zn, from waste PDP glass, electro-kinetic process was introduced and factors that affect heavy metal removing rate were investigated. Results showed that HNO₃ concentration and PDP adding amount could significantly impact heavy metal removing rate, while current density was on the opposite. Heavy metal removing rate increased first and then decreased as the time extension. When PDP powders was 2 g, 9 mL 5 mol/L HNO₃ was added, current density was 200 mA/cm² and time was 6 h, the removal rate of As, Ba, Cu, Zn were 71.02%, 95.87%, 92.50% and 97.70%, respectively. As, Ba, Cu and Zn distributions in the cathode, anode and middle chamber varied as changing particle size, HNO₃ concentration, current density. Generally, most Cu was concentrated in cathode chamber, and Zn in the anode chamber, while As and Ba would be in both cathode and anode chamber. As, Ba, Cu and Zn, in the middle chamber, no more than 10%, were the lowest among the three.

Abstract: Precious metals are used widely in electronic industry because of their excellent heat resistance, corrosion resistance and catalytic property. Therefore it is important to recycle precious metals from E-waste. In this study, a new amid extractant N,N-Dimethyl-N,N-didecyl-3-thiopentanediamide (MDTDGA) was firstly synthesized through N-alkylated and N-acylation reaction. The extraction behavior of precious metals with MDTDGA in 80% dodecane-20% 2-ethylhexanol from hydrochloric acid was studied. The extraction ration increases with HCl concentration and extractant concentration, but it is not influenced by H⁺ concentration. It is indicated that the extraction of precious metals Pd (II), Pt (IV), Au (III) with MDTDGA is neutral coordination. High extraction efficiency of Au (III) of 99.5% using MDTDGA was obtained.

Abstract: In electronic waste recycling industry, printed wire boards (PWBs)/integrated chips (ICs) recycling is one of the most challenge tasks due to the fact that PWBs/ICs are diverse and complex in terms of materials and components makeup,as well as the original equipment manufacturing processes. In this paper, we will present environmental benign solution to recover valuable metals from PWB and integrated circuit chips (ICs) dissembled from waste PWB, based on green chemistry methodologies. We will demonstrate that the process/chemistry can selectively separate and recover precious metals from base metals. The 95%-99% recovery rate of precious metals can be achieved from the recycling of PWB and integrated circuit chips.

Abstract: Waste printed circuit boards (PCBs) contain toxic metals at concentrations that could pose human and environmental threats if improperly disposed of. Also, PCBs are known to contain appreciable quantities of precious metals with economic value. This study investigated the levels of Cu, Pb, Ni, Zn and Cd in the PCBs extracted from ten discarded laptops and outlined the trends that can be drawn from the results. The laptops were made by a world-wide leading original equipment manufacturer (OEM). The whole laptops were disassembled to enable the extraction of populated PCBs; components were dismounted and all de-populated PCBs were separately crushed, sieved, and total recoverable metals aforementioned were extracted using EPA 3050B method. Also, PCBs were analysed following the EPA Toxicity Characteristic Leaching Procedure (TCLP) and the EPA Synthetic Precipitation Leaching Procedure (SPLP) tests to study their leachability when exposed to municipal landfill and rain water, respectively. The extracts were analysed for metal levels using atomic absorption spectrophotometric technique. The sequence of total recoverable metals was Cu (3.23±0.41%) > Pb (1.95±0.57%) > Ni (0.88±0.36%) > Zn (0.012±0.003%) > Cd (4.00±2.30 mg/kg). Our study revealed a reduction in average % Cu and Zn by at least 6 and 1.5 times, respectively compared with previous studies. The level of Pb also was noticed to decrease from 2.5% in PCBs produced in 2006 to 1.7% in those produced in 2009. On the one hand, this could be a sign of the efforts conducted by OEMs to shift towards the design of eco-friendly products. On the other hand, average Pb (mg/L) level in TCLP and SPLP leachates was respectively 13 and 11 times higher than EPA limit of 5mg/L. Discarded laptop PCBs should still be handled and disposed of as hazardous waste.

Abstract: As 10 years have passed since the Japanese home electrical appliance recycling system came into operation, the results of the system have become clearer, and it is therefore time for us to analyze and evaluate its performance in terms of both the environment and the economy. The system covers 4 specified house appliances, and although roughly 2/3 of these discarded appliances are collected and recycled formally by the manufactures, the greater part of the remaining 1/3 is exported as used items or scrap. Consequently, the government has issued guidelines for the reuse and recycling as countermeasures against illegal dumping and to regulate the export of e-scrap.

Abstract: The increasing amount of kitchen waste (KW) has raised great concerns for the environmental risk and health issues. It is necessary that some technologies are utilized for managing and treating KW. For proper technology and operation of treating KW, the general composition characteristics of KW were investigated in accordance with different catering types. KW from different catering types (Restaurant, Noshery, Snack bar and Canteen) in Shanghai was sampled for each season in a year. All sampling was carried out 3 days repeatedly and performed after pre-treatment in order to obtain more homogeneous and representative samples. The moisture and VS/TS ratio of KW for different catering types is more than 70% and 89%, respectively. High VS/TS value indicates that KW is suitable for composting and biodegradation. The pH value of KW is lower than 7 for each catering type and drink shop gets the lowest pH (3.47). The total amount of fat, protein and carbonhydrate is over 90% for all the samples and high content of fat and protein indicates that KW can be used as the raw materials for feed process.

Abstract: On the basis of OCED Guideline 106, batch sorption studies were employed to reveal sorption of atrazine by amending biochar in tropical soils, namely, laterite, paddy soil and dry red soil. Biochar,a micro-porosity and great surface product, was generated by pyrolysis of manioc wastes at 750°C(BC750) and modified substances (MC750) were produced by loading Fe³⁺. The mechanism of sorption was examined by charactering BC750 and MC750. In this study, carbonization can improve aromaticity, specific surface and alkaline groups of biomass. The isotherms of atrazine in soil seemed closed to linear with partition, whereas the sorption of atrazine in biochar-added soil was a mainly pore-filling mechanism to exhibit nonlinearity. Temkin model was satisfactorily analyzed the sorption isotherm of atrazine by BC750/MC750 into soil with R² between 0.92~0.998. HI of all the sorbents were greater than 1, which indicated that the desorption rate was higher than the sorption rate. BC750/MC750 had a greater affinity for atrazine in soil than that of unamended soil. And the sorption capacity of unmodified biochar is slightly less than modified biochar, but the desorbed amounts of atrazine are less. Results indicated that biochars derived from agricultural wastes can play a crucial role in the removal of hydrophobic organic chemicals.

Abstract: To study the biochar properties and its influence on Cu (II) adsorption, biochar was prepared from bagasse under the conditions of 350°C, 450°C and 550°C respectively, and biochar was added to three typical tropical soils (paddy soil, laterite and dry red soil). After mixed culture for 30 d, batch equilibrium experiment method was used to determine the effect of biochar on soil adsorption of Cu (II) before the characterization of biochar properties. Results showed that ash content, CEC and pH value of were increased with the increase of pyrolysis temperature. PH values ranged from 5.56 to 8.92. Moreover, the specific surface area and pore structure were affected by pyrolysis temperature. In addition, when biochar was added into soils, the adsorption capacity of Cu (II) in paddy soil, laterite and dry red soil increased by 85.98%, 89.07% and 94.73% respectively. Freundlich and Langmuir equation could be fit for adsorption isotherm of Cu (II). Results demonstrated that the Freundlich model (R²>0.976) was the better isotherm than Langmuir model (R²>0.917).

Abstract: Densified biomass pellets named as H/S-BPs were prepared from waste wood sawdust (S) in the presence of water hyacinth fiber (H) as solid bridge under room temperature and 6 MPa lower than in the previous study. Mechanical properties including relaxed density (ρ_r), resiliency (R), abrasion resistance (AR) and impact resistance index (IRI) were evaluated. Results showed that adding H greatly reduced negative effect of resiliency on the mechanical properties of H/S-BPs during storage. For example, H/S-BPs compressed at 6 MPa in an H/S mass ratio of 1 to 3 presented lower resiliency of 10% and higher relaxed density of 1.04 kg dm^-3 than pellets without H fiber. This is due to the intertwining action of H fiber, what fabricates solid bridge, replacing the bonding creating by applying high pressure to resist the disruptive force caused by elastic recovery. Thus, compression of waste H and S in a mass ratio of 1 to 3 at room temperature under 6 MPa is a cost-effective process to produce densified sustainable bio-fuel pellet as well as dispose waste S and H, combining the economical and environmental benefits.

Abstract: Food residue is receiving increasing attention because of its large quantity of production, wide generation and potential environmental hazards. The characteristics of food residue vary greatly with catering habits. In order to study the composition characteristics of food residue, and to determine the reasonable treatment technologies, ten types of catering habits in Shanghai were sampled, and experimental research was conducted by means of analyzing the variation of moisture content, volatile solid, C/N ratio, salt content and metal elements. The results showed that moisture content varied greatly in accordance with catering habits, while VS/TS ratio was comparatively stable, ranging from 90.60% to 96.17%. The C/N ratio and salt content fluctuated with the change of catering habits, and the highest value was from Sichuan cuisine restaurants and local cuisine restaurants, respectively. Among the four metal elements, Mg had the highest content, followed by Al, and both Fe and Zn accounted for little content in food residue.