In-Depth Study on the Effects of Impurity Ions in Saline Wastewater Electrolysis.

Concentration followed by electrolysis is one of the most promising ways for saline wastewater treatment, since it could produce H2, Cl2, and an alkaline solution with deacidification potential. However, due to the diversity and difference of wastewater, knowledge on the suitable salt concentration for wastewater electrolysis and the effects of mixed ions are still lacking. In this work, electrolysis experiments of mixed saline water were conducted. The salt concentration for stable dechlorination was explored, with in-depth discussions on the effects of typical ions such as K+, Ca2+, Mg2+, and SO42-. Results showed that K+ had a positive effect on the H2/Cl2 production of saline wastewater through accelerating the mass transfer efficiency in the electrolyte. However, the existence of Ca2+ and Mg2+ had negative effects on the electrolysis performance by forming precipitates, which would adhere to the membrane, reduce the membrane permeability, occupy the active sites on the cathode surface, and also increase the transport resistance of the electrons in the electrolyte. Compared to Mg2+, the damaging effect of Ca2+ on the membrane was even worse. Additionally, the existence of SO42- reduced the current density of the salt solution by affecting the anodic reaction while having less of an effect on the membrane. Overall, Ca2+ ≤ 0.01 mol/L, Mg2+ ≤ 0.1 mol/L and SO42- ≤ 0.01 mol/L were allowable to ensure the continuous and stable dechlorination electrolysis of saline wastewater.

Investigation and improvement of the desulfurization performance of molten carbonates under the influence of typical pyrolysis gases.

Co-pyrolysis with oxygen-lean waste tires could improve the quality of pyrolytic oil from the bio-wastes while H2S/COS generated during co-pyrolysis process has a negative impact on the utilization of oil/syngas as well as the flue gas pollution control. Compared to traditional wet desulfurization process, high-temperature desulfurization via molten carbonates could reduce heat loss and favor the recycling of captured sulfur. Notably, small-molecule pyrolytic gases might change the species of sulfur-containing gases and promote the re-emission of absorbed sulfur from the molten salts. To fully understand the effects of pyrolysis gases (H2/CO/H2O/CO2) on molten salts desulfurization efficiency as well as mutual conversion mechanism of H2S and COS, equilibrium compositions calculations and adsorption experiments were carried out in the present study. The results showed that H2/CO had few effects on molten salts desulfurization performance and mutual conversion of H2S/COS. In contrast, CO2 and H2O had obvious adverse effects on desulfurization efficiency through the transferring of free S2- into emitted sulfur-containing gases. More specifically, only a small amount of CO2 reacted with S2- to produce COS while more S2- was converted to H2S and released from the reactor outlet when H2O was introduced. Fortunately, the impact of H2O or CO2 on molten salts desulfurization could be weakened with the addition of CaCO3 by transferring the molten free S2- into precipitated CaS. Besides, multi-stage desulfurization units connected in series and parallel were proposed and estimated, which was confirmed to show good performance to maintain the high desulfurization efficiency from the complicated pyrolytic gases.

Bioremediation of heavy metal contaminated aqueous solution by using red algae Porphyra leucosticta.

Bioremediation is an effective process for the removal and recovery of heavy metal ions from aqueous solutions. In this study, red algae Porphyra leucosticta was examined to remove Cd(II) and Pb(II) ions from wastewater through biological enrichment and biological precipitation. The experimental parameters that affect the bioremediation process such as pH, contact time and biomass dosage were studied. The maximum bioremediation capacity of metal ions was 31.45 mg/g for Cd(II) and 36.63 mg/g for Pb(II) at biomass dosage 15 g/L, pH 8.0 and contact time 120 minutes containing initial 10.0 mg/L of Cd(II) and 10.0 mg/L of Pb(II) solution. Red algae Porphyra leucosticta biomass was efficient at removing metal ions of 10.0 mg/L of Cd(II) and 10.0 mg/L of Pb(II) solution with bioremediation efficiency of 70% for Cd(II) and 90% for Pb(II) in optimal conditions. At the same time, the removal capacity for real industrial effluent was gained at 75% for 7.6 mg/L Cd(II) and 95% for 8.9 mg/L Pb(II). In conclusion, it is demonstrated that red algae Porphyra leucosticta is a promising, efficient, cheap and biodegradable sorbent biomaterial for reducing heavy metal pollution in the environment and wastewater.

Leaching of spent lead acid battery paste components by sodium citrate and acetic acid.

A sustainable method, with minimal pollution and low energy cost in comparison with the conventional smelting methods, is proposed for treating components of spent lead-acid battery pastes in aqueous organic acid(s). In this study, PbO, PbO2, and PbSO4, the three major components in a spent lead paste, were individually reacted with a mixture of aqueous sodium citrate and acetic acid solution. Pure lead citrate precursor of Pb3(C6H5O7)2 · 3H2O is the only product crystallized in each leaching experiment. Conditions were optimized for individual lead compounds which were then used as the basis for leaching real industrial spent paste. In this work, efficient leaching process is achieved and raw material cost is reduced by using aqueous sodium citrate and acetic acid, instead of aqueous sodium citrate and citric acid as reported in a pioneering hydrometallurgical method earlier. Acetic acid is not only cheaper than citric acid but is also more effective in aiding dissolution of the lead compounds thus speeding up the leaching process in comparison with citric acid. Lead citrate is readily crystallized from the aqueous solution due to its low solubility and can be combusted to directly produce leady oxide as a precursor for making new battery pastes.

Preparation and characterization of nano-structured lead oxide from spent lead acid battery paste.

As part of contribution for developing a green recycling process of spent lead acid battery, a nanostructural lead oxide was prepared under the present investigation in low temperature calcination of lead citrate powder. The lead citrate, the precursor for preparation of this lead oxide, was synthesized through leaching of spent lead acid battery paste in citric acid solution. Both lead citrate and oxide products were characterized by means of thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The results showed that the lead citrate was sheet-shape crystal of Pb(C(6)H(6)O(7)) · H(2)O. When the citrate was calcined in N(2) gas, ß-PbO in the orthorhombic phase was the main product containing small amount of Pb and C and it formed as spherical particles of 50-60 nm in diameter. On combusting the citrate in air at 370°C (for 20 min), a mixture of orthorhombic ß-PbO, tetragonal α-PbO and Pb with the particle size of 100-200 nm was obtained, with ß-PbO as the major product. The property of the nanostructural lead oxide was investigated by electrochemical technique, such as cyclic voltammetry (CV). The CV measurements presented the electrochemical redox potentials, with reversibility and cycle stability over 15 cycles.