Effect of substitution reaction with tin chloride in thermal treatment of mercury contaminated tailings.

Sites contaminated by mercury (Hg) from artisanal small-scale gold mine tailings have been found near agricultural land. For the active implementation of the Minamata Convention on Mercury, development of technology for the remediation of Hg contaminated sites is required. This study examined the conditions for the thermal treatment of Hg contaminated tailings at reduced temperature by introducing SnCl2 as an additive. Thermogravimetric analysis (TGA) was used to identify the possibility of converting typical Hg compounds (HgO, HgS) in the environment to HgCl2. The operation conditions for thermal treatment such as temperature, retention time, and ratio of [Cl2]/[Hg] were derived from lab scale experiments using commercial Hg compounds (HgO, HgS), additive (SnCl2), and tailings. The tailings with Hg content of 26.39 mg-Hg/kg were reduced to 3.87 mg-Hg/kg and 4.57 µg-g/L of leaching concentration through the application of the Korea standard leaching test. Both concentrations were below the standard limit of soil pollution and hazardous waste classification criteria. The sequential extraction procedure was applied to evaluate the Hg stability of residual tailings. The results show that this method will be effective for remediation of small scale Hg contaminated areas.

The effect of NaOH for the recovery of elemental mercury from simulated mixture wastes and waste sludge from an industrial process using a thermal desorption process.

The need for appropriate management of mercury (Hg) wastes is increasing for active implementation of the Minamata Convention on Mercury. Though Hg can be a contaminant if it is not dealt with properly, recovered Hg can become a resource. Besides, a recovered Hg with reduced volume can be managed efficiently. This study examined the effect of NaOH for the recovery of elemental Hg from a waste sludge from an industrial process using the thermal desorption and condensation. For this purpose, the operating conditions, including temperature and pressure of the apparatus, were derived based on the experiments using Hg compounds (HgS and HgO), simulated waste (mixtures of HgCl2/As2O3 and HgS/As2O3). The reduced chamber pressure promoted to the recovery of elemental Hg via the thermal desorption. NaOH was introduced to increase the recovery efficiency of Hg in the presence of interfering substances such as S and As compounds. The Hg recovery efficiency increased, and 62.5% of Hg was recovered as elemental form by adding NaOH via thermal desorption and gas condensation with a lab-scale apparatus. Interfering substances such as Cl, S, and As compounds were captured in the bottom ash when bound with Na.

Correlation between mercury content and leaching characteristics in waste phosphor powder from spent UV curing lamp after thermal treatment.

This study evaluated the correlation between the amount of mercury (Hg) compounds in waste phosphor powder from spent UV curing lamps and their leaching characteristics. The appropriate thermal treatment conditions and Hg content in the residue necessary to satisfy the leaching criteria for classification as non-hazardous waste were identified. The decomposition of Hg compounds by thermal treatment was also evaluated by comparing sequential extraction results based on thermal stability and leaching potential of Hg compounds. Before the thermal treatment, the Hg content in waste phosphor powder and concentration in the leaching extract were 108.7 mg-Hg/kg and 0.56 mg-Hg/L, respectively. Hg compounds with low thermal stability were removed rapidly during the initial stage of thermal treatment at temperatures between 400 °C and 600 °C. After thermal treatment, Hg in the form of an intermetallic compound, such as Sr-Hg, was expected to be remained mainly, and the Hg content was reduced to 13 mg-Hg/kg in the waste phosphor powder, at that point the residue satisfied the leaching standard limit (5 µg-Hg/L) for non-hazardous waste stipulated in the legislation of Republic of Korea.

Application of powdered activated carbon coating to fabrics in a hybrid filter to enhance mercury removal.

Elemental mercury (Hg0) is predominant constituent of flue gas emitted from coal-fired power plants. Adsorption has been considered the best available technology for removal of Hg0 from flue gas. However, adsorbent injection increases the amount of ash generated. In the present study, powdered activated carbon (PAC) was coated on polytetrafluoroethylene/glass fiber filters to increase Hg0 removal while concurrently reducing the amount of ash generated. The optimal PAC coating rate was determined in laboratory experiments to ensure better Hg0 removal with low pressure drop. When PAC of particle size less than 45 µm was used, and the areal density was 50 g/m2, the pressure drop remained under 30 Pa while the Hg0 removal efficiency increased to 15.8% from 4.3%. The Hg0 removal efficiency also increased with decrease in filtration velocity. The optimal PAC coating rate was applied on a hybrid filter (HF), which was combined with a bag filter and an electrostatic precipitator in a single chamber. Originally designed to remove fine particulates matter, it was retrofitted to the flue gas control device for simultaneous Hg0 removal. By employing the PAC coating, the Hg removal efficiency of the HF increased to 79.79% from 66.35%. Also, a temporary reduction in Hg removal was seen but this was resolved following a cleaning cycle in which the dust layer was removed.

The simultaneous capture of mercury and fine particles by hybrid filter with powder activated carbon injection.

The hybrid filter (HF) was newly designed and operated with powder activated carbon (PAC) injection to capture mercury and fine particulate matter in the coal power plant. With PAC injection in HF operation, the capture efficiency of elemental mercury was clearly enhanced. When the injection rate of PAC increased from 0 to 20 mg/m3, the speciation fraction of elemental mercury significantly decreased from 85.19% to 3.76% at the inlet of the hybrid filter. The speciation fraction of oxidized mercury did not vary greatly, whereas the particulate mercury increased from 1.31% to 94.04%. It was clearly observed that the HF played a role in the capture of mercury and fine PM by leading the conversion of elemental mercury as particulate mercury and the growth of PM via electrode discharge in the HF operation with PAC injection.

Mercury distribution characteristics in primary manganese smelting plants.

The mercury (Hg) distribution characteristics were investigated in three primary manganese smelting plants in Korea for the assessment of anthropogenic Hg released. Input and output materials were sampled from each process, and Hg concentrations in the samples were analyzed. Among the input materials, the most mercury was found in the manganese ore (83.1-99.7%) and mercury was mainly released through fly ash or off gas, depending on the condition of off gas cleaning system. As off gas temperature decreases, proportion and concentration of emitted gaseous elemental mercury (Hg0) in off gas decreases. Based on mass balance study from these three plants and national manganese production data, the total amount of mercury released from those Korean plants was estimated to 644 kg/yr. About half of it was emitted into the air while the rest was released to waste as fly ash. With the results of this investigation, national inventory for Hg emission and release could be updated for the response to Minamata Convention on Mercury.