Evaporation of mercury from domestic waste leachate

An experimental study has been made of the rate at which dissolved mercury is lost from domestic waste leachate by evaporation from the air leachate in     

Amalgamation mechanism in dental amalgam alloys

Model experiments to explore the amalgation mechanism in conventional Ag₃Sn and high copper single-composition dental alloys have been conducted by rotating alloy roda in liquid mercury at different speeds and for different durations. After removing the rod from the mercury, the vacuum volatilization technique was used to accelerate the supersaturation of dissolved elements in the liquid mercury. The surface and sectional scanning electron microscope (SEM) views give direct evidence for new amalgamation mechanism in high copper dental alloys. The amalgamation reaction begins with the selective dissolution of the Ag₃Sn phase in mercury, tin gettering to the crumbled-off Cu₃Sn phase, heterogeneous nucleation of the Cu₆Sn₅ phase on the seed of the crumbled-off Cu₃Sn phase and was followed by the nucleation of the Ag₂Hg₃ phase. The unexplained phenomena, the formation of the -2 phase (Sn_7-8Hg) in higher content of mercury and the nonexistence of the -2 phase in higher content of copper alloys such as Sybralloy, were clearly understood by applying the new model.     

Influence of thermal treatments on Ag Sn Cu powders in order to reduce mercury contents in dental amalgam

The mercury content of dental amalgams is a controversial subject with regard to the biological properties of these materials. The object of this study is to optimize the thermal treatments performed on an experimental powder in order to obtain a low mercury ratio (41% by weight) while preserving the desirable clinical qualities of the material. Using atomized powder, two types of thermal treatments are performed: A1, to obtain a partially annealed structure and A2, to obtain a complete homogenization. The kinetics of the amalgamation reaction is mainly evaluated by X-ray diffraction to identify the newly formed phases as a function of setting time. Mechanical properties are evaluated according to the ISO norms at 37 °C. Metallographical examination of the amalgams shows a «Ag-Hg» phase which acts as a matrix incorporating the «Cu-Sn» and «Ag-Sn» compounds. The setting kinetics of the A1 amalgams is linear and slightly more rapid than that of the A2 amalgam. The mechanical properties of the amalgams are significantly improved regarding the higher mercury content commercial amalgams. A specific thermal treatment permits us to slow down the diffusion of mercury between the different intermetallic compounds into the powder. The final amalgam composition, thus, most approaches the stoechiometric ratio calculated from a quaternary diagram.     

The matrix phase of a ductile dental amalgam

In this study, the ternary HgAgSn-₁ matrix of a ductile dental amalgam has been characterized and compared with that of a brittle amalgam. Specimens of both amalgams were prepared form commercial alloy powders according to the ADA specification 1, stored at 37°C and studied by differential scanning calorimetry technique at timed intervals up to 1 year. Experimental amalgams of AgCu eutectic admixed with varying concentrations of Sn were used as standards. The matrix of the ductile amalgam was found to contain two substructures initially. One was saturated with Sn and the other contained lesser amounts of Sn. These substructures disappeared with time leading to a matrix in which Sn was well below its saturation limit but uniformly distributed. The matrix of the brittle amalgam, on the other hand, was saturated with Sn during the entire period of this study.     

Location of zinc in a conventional dental amalgam matrix

The location of zinc in a conventional dental amalgam matrix has been studied by electroetching, scanning electron microscopy and energy-dispersive X-ray analysis. It has been shown that zinc is randomly and non-uniformly distributed in the matrix phases. The major portion of zinc is segregated as an intergranular structure at ₁, and ₂ grain boundaries. A zinc-containing substructure has been observed in ₂ but not in ₁. A small amount of zinc may exist as solid solution in both phases.     

Recovery of isopropyl alcohol from waste solvent of a semiconductor plant

An important waste solvent generated in the semiconductor manufacturing process was characterized by high isopropyl alcohol (IPA) concentration over 65%, other organic pollutants and strong color. Because of these characteristics, IPA recovery was deemed as a logic choice for tackling this waste solvent. In the present work, an integrated method consisting of air stripping in conjunction with condensation and packed activated carbon fiber (ACF) adsorption for dealing with this waste solvent. The air stripping with proper stripping temperature control was employed to remove IPA from the waste solvent and the IPA vapor in the gas mixture was condensed out in a side condenser. The residual IPA remaining in the gas mixture exiting the side condenser was efficiently removed in a packed ACF column. The air stripping with condensation was able to recover up to 93% of total IPA in the initial waste solvent. The residual IPA in the gas mixture, representing less than 3% of the initial IPA, was efficiently captured in the packed ACF column. Experimental tests were conducted to examine the performances of each unit and to identify the optimum operating conditions. Theoretical modeling of the experimental IPA breakthrough curves was also undertaken using a macroscopic model. The verified breakthrough model significantly facilitates the adsorption column design. The recovered IPA was found to be of high purity and could be considered for reuse.     

Recovery of nitric acid from waste etching solution using solvent extraction

As part of our efforts to identify effective ways and means to keep source water safe, the concept of risk assessment and management is introduced in this paper to address the issue of risk assessment and management of arsenic in source water in China. Carcinogenic and non-carcinogenic risk are calculated for different concentrations of arsenic in source water using the corrective equation between potential health risk and concentration of arsenic in source water with purification process taken into consideration. It is justified through analyses that risk assessment and management is suitable for China to control pollution of source water. The permissible content of arsenic in source water should be set at 0.01 mg/L at present in China, and necessary risk management measures include control contaminated sources and improvement of purification efficiency.     

Plasmonic detection of mercury via amalgam formation on surface-immobilized single Au nanorods

Abstract

Au nanorods were used as plasmonic transducers for investigation of mercury detection through a mechanism of amalgam formation at the nanorod surfaces. Marked scattering color transitions and associated blue shifts of the surface plasmon resonance peak wavelengths (λ_max) were measured in individual nanorods by darkfield microscopy upon chemical reduction of Hg(II). Such changes were related to compositional changes occurring as a result of Hg–Au amalgam formation as well as morphological changes in the nanorods’ aspect ratios. The plot of λ_max shifts vs. Hg(II) concentration showed a linear response in the 10–100 nM concentration range. The sensitivity of the system was ascribed to the narrow width of single nanorod scattering spectra, which allowed accurate determination of peak shifts. The system displayed good selectivity as the optical response obtained for mercury was one order of magnitude higher than the response obtained with competitor ions. Analysis of mercury content in river and tap water were also performed and highlighted both the potential and limitation of the developed method for real sensing applications.     

Stress protein assay for the evaluation of cytotoxicity of dental amalgam

To evaluate the cytotoxicity of mercury in dental amalgams, a stress protein assay was performed and the results were compared with the cytotoxicity evaluated by a neutral red uptake assay. The induction of a major stress protein, hsp70, was analyzed at levels of mRNA, synthesis and accumulation in human HeLa cells treated with extracts from amalgam, metal mercury and mercuric chloride. Mercuric chloride induced an increase in the synthesis of hsp70 at concentrations of mercury half those used for the neutral red uptake assay. The extracts from dental amalgam and metal mercury induced an increase in hsp70 mRNA at concentrations of mercury half those causing the inhibition of neutral red uptake into cells. Furthermore, the extracts from dental amalgam or metal mercury increased the synthesis of hsp70 and inhibited the uptake of dye at concentrations of mercury 1/10-1/50 lower than those at which mercuric chloride acted. These results suggest that the stress protein assay is more sensitive than the conventional neutral red assay for the evaluation of the cytotoxicity of mercury in dental amalgams and that the methods used in the preparation of metal solutions seem to be critical to the evaluation of cytotoxicity of dental materials.     

Fracture toughness and critical strain energy release rate of dental amalgam

Fracture toughness, critical strain energy release rate and critical stress intensity factor were determined for lathe-cut, spherical, admixed, and two atomized high-copper dental amalgams. At a loading rate of 0.005cm min^–1 for 24-hour samples, the spherical amalgam had the highest resistance to unstable crack propagation. At a loading rate of 0.05cm min^–1 for both 24-hour and one-month samples, the lathe-cut amalgam had the highest resistance to unstable crack propagation. One of the atomized high copper amalgams showed the lowest resistance to crack propagation. The values were consistent with data obtained in single-pass wear studies.     

扩散渗析法回收湿法炼铜厂电解贫液中的硫酸

采用扩散渗析法回收福建某湿法炼铜厂电解贫液中的硫酸.电解贫液经"砂滤保安过滤扩散渗析"处理,回收酸返回"萃取电积"工段,残液送至堆浸循环使用.投产一年半来,已累计回收硫酸3 929.29t,充分回收利用资源,实现循环经济,创造明显的经济效益,解决了该厂电解贫液的开路难题.     

Recovery of sulfuric acid from waste aluminum surface processing solution by diffusion dialysis

Diffusion dialysis with anionic ion exchange membranes was employed to recover sulfuric acid from the waste acid solution of aluminum surface processing plant. Experiments were conducted to examine the dialyzer performances under various operating conditions, including feed flow rates, sulfuric acid concentration in the feed solution, temperature and number of pieces of ion exchange membrane. Diffusion dialysis was found very efficient for this purpose. Based on the test results, optimum operating conditions of these variables were identified. Preliminary economic evaluation of the process indicated that diffusion dialysis is highly viable for sulfuric acid recovery due to its short payback period.     

Effect of heat treatment on structure and properties of dispersed-type dental amalgam

Effect of heat treatment of Ag–Cu–Pd dispersant particles on the structure, mechanical properties and mercury vapor release rate of an Ag–Cu–Sn/Ag–Cu–Pd-based dental amalgam has been investigated. Experimental results indicate that crystallinity of dispersant Ag-Cu–Pd alloy increases with increasing HTT, with most notable increase occurring between 100 and 200 °C. Increasing HTT of Ag–Cu–Pd alloy does not change much of the mercury/alloy ratio for amalgamation, but largely reduces working/setting time of the amalgam. The Ag–Cu–Pd particles in 7 d-aged amalgam are comprised primarily of an outer Sn/Cu/Pd-rich zone and an inner Ag/Cu/Pd-rich zone with eutectic-type morphology and chemical distribution. The annealing-enhanced Pd segregation effect is most significantly observed in the amalgam derived from 300 °C-annealed Ag–Cu–Pd dispersant. This amalgam also has the highest compressive strength, highest DTS, and lowest creep rate. Higher annealing temperature causes mechanical property of the amalgam to deteriorate. The initial mercury vapor release rates of amalgams derived from 100, 200 and 300 °C-annealed Ag–Cu–Pd dispersant are significantly lower than that derived from 400 °C-annealed dispersant.     

The failure of amalgam dental restorations due to cyclic fatigue crack growth

In this study a restored mandibular molar with different Class II amalgam preparations was examined to analyze the potential for restoration failure attributed to cyclic fatigue crack growth. A finite element analysis was used to determine the stress distribution along the cavo-surface margin which results from occlusal loading of each restoration. The cyclic crack growth rate of sub-surface flaws located along the dentinal cavo-surface margin were determined utilizing the Paris law. Based on similarities in material properties and lack of fatigue property data for dental biomaterials, the cyclic fatigue crack growth parameters for engineering ceramics were used to approximate the crack growth behavior. It was found that flaws located within the dentine along the buccal and lingual margins can significantly reduce the fatigue life of restored teeth. Sub-surface cracks as short as 25 m were found capable of promoting tooth fracture well within 25 years from the time of restoration. Furthermore, cracks longer than 100 m reduced the fatigue life to less than 5 years. Consequently, sub-surface cracks introduced during cavity preparation with conventional dental burrs may serve as a principal source for premature restoration failure. ©©1999©Kluwer Academic Publishers     

Recovery of H2SO4 from waste acid solution by a diffusion dialysis method

A diffusion dialysis method using anion exchange membrane was used to recover H2SO4 from waste sulfuric acid solution produced at the diamond manufacturing process. Effects of flow rate, operation temperature, and metal ion concentration on the recovery of H2SO4 were investigated. The recovery of H2SO4 increased with the concentration of H2SO4 and operation temperature. It also increased with the flow rate ratio of water/H2SO4 solution up to 1, above which no further increase was observed. The flow rate did not affect the rejection of Fe and Ni ions. About 80% of H2SO4 could be recovered from waste sulfuric acid which contained 4.5M free-H2SO4 at the flow rate of 0.26x10(-3) m3/hm3. The concentration of recovered H2SO4 was 4.3M and the total impurity was 2000 ppm. Preliminary economic evaluation has revealed that the dialysis system is highly attractive one that has payback period of only few months.     

Recovery of metal fractions from waste printed circuit boards via the vibrated gas-solid fluidized bed

The vibrated gas-solid fluidized bed based on fluidized separation technology was used to recycle the metallic fraction of waste printed circuit boards (WPCBs). The size fraction composition and element distribution of the crushed products were analyzed by sieving and X-ray fluorescence, respectively. The contents of Cu, Zn, Fe and Ti in various size fractions had significant differences, resulting in preliminary enrichment. The performance of vibration on the fluidization characteristics of WPCBs powder was described. With fluidization number, vibration frequency and vibration amplitude as variables, the separation performance of WPCBs powder under various operational conditions was studied. With the optimum operated conditions, the optimal recovery rates of metallic fraction of the three size fractions of 1–0.5 mm, 0.5–0.25 mm and 0.25–0.125 mm were 88.53%, 95.61% and 82.28%, respectively. The vibrated gas-solid fluidized bed can effectively enrich and recover the metallic fraction of WPCBs, providing convenience for subsequent separation.     

Effect of placing,removing and polishing of amalgam restorations on 24-h urinary mercury concentration

Twenty-four-hour urinary mercury concentration were assessed in 43 patients before and after removing old amalgam fillings (8 pts), placing (13 pts), and polishing of amalgam (22 pts). Baseline analyses 8 days before the treatments showed on average 18.5±7.2 g mercury mass excreted per 24-h urine samples. The removal of old fillings caused a total excreted mass of 56.3±32.3 g Hg, the placing of amalgam 45.9±26.2 g Hg, and the polishing 56.25±33.77 g Hg, respectively, one day after the treatments. When compared with the baseline values, the urinary mass excreted remained significantly elevated during the 8-day follow-up. However, all Hg values measured were below the WHO recommandations for the threshold limits for urinary mercury.     

Recovery of metals from waste printed circuit boards by a mechanical method using a water medium

Research on the recycling of waste printed circuit boards (PCB) is at the forefront of environmental pollution prevention and resource recycling. To effectively crush waste PCB and to solve the problem of secondary pollution from fugitive odors and dust created during the crushing process, a wet impacting crusher was employed to achieve comminution liberation of the PCB in a water medium. The function of water in the crushing process was analyzed. When using slippery hammerheads, a rotation speed of 1470 rpm, a water flow of 6 m³/h and a sieve plate aperture of 2.2 mm, 95.87% of the crushed product was sized less than 1 mm. 94.30% of the metal was in this grade of product. Using smashed material graded −1 mm for further research, a Falcon concentrator was used to recover the metal from the waste PCB. Engineering considerations were the liberation degree, the distribution ratio of the metal and a way to simplify the technology. The separation mechanism for fine particles of different densities in a Falcon concentrator was analyzed in detail and the separation process in the segregation and separation zones was deduced. Also, the magnitude of centrifugal acceleration, the back flow water pressure and the feed slurry concentration, any of which might affect separation results, were studied. A recovery model was established using Design-Expert software. Separating waste PCB, crushed to −1 mm, with the Falcon separator gave a concentrated product graded 92.36% metal with a recovery of 97.05%. To do this the reverse water pressure was 0.05 MPa, the speed transducer frequency was set at 30 Hz and the feed density was 20 g/l. A flow diagram illustrating the new technique of wet impact crushing followed by separation with a Falcon concentrator is provided. The technique will prevent environmental pollution from waste PCB and allow the effective recovery of resources. Water was used as the medium throughout the whole process.