Combined Electrodialysis and Electrocoagulation as Treatment for Industrial Wastewater Containing Arsenic and Copper.

In copper smelting processes, acidic effluents are generated that contain inorganic contaminants such as arsenic and copper. Nowadays, the treatment of wastewater is done by physicochemical methods without copper recovery. Electrodialysis is an alternative process that can recover copper. Moreover, when electrocoagulation is applied to remove arsenic from wastewater, a more stable final sludge of less volume is obtained. The present research studies the application of a combined electrodialysis and electrocoagulation process to (1) recover Cu and (2) precipitate and remove arsenic simultaneously in the same batch reactor, using synthetic wastewater that simulates wastewater from a copper smelter. Copper and arsenic could be removed and separated by the electrodialysis part, and the electrocoagulation of arsenic was verified. With electrodialysis, the arsenic and copper removals were 67% and 100%, respectively, while 82% of the arsenic arriving at the electrocoagulation part of the cell could be precipitated and removed by this process. Initial concentrations were around 815 mg L-1 Cu and 7700 mg L-1 As. The optimal current was found to be 1.36 A due to the shorter treatment times necessary to get removal percentages, recovery percentages and energy/removed copper mass ratios in the same ranges as the values achieved with a current of 1.02 A. In summary, the combined process is a promising tool for simultaneous copper recovery and arsenic removal.

Removal of Heavy Metals from Mine Tailings in Central Chile Using Solidago chilensis Meyen, Haplopappus foliosus DC, and Lycium chilense Miers ex Bertero.

Mining activities have been a part of the history of Chile since time immemorial, generating pollution and environmental liabilities. Due to the lack of regulation, many tailings are deposited close to rivers or/and on unstable ground, near which towns have been built, generally in locations with no budget for their treatment. This study tested three plant species from Northern and Central Chile to remove total chromium, nickel, and zinc from tailings: Solidago chilensis, Haplopappus foliosus, and Lycium chilense, which complements the few existing studies on heavy metals removal with native or endemic Chilean shrubs. The experiments were conducted ex situ, and the initial and final concentrations of metals were determined in tailings and plants to obtain the removal efficiency, translocation and bioconcentration factors. Among these species, the best performance was obtained using Solidago chilensis, achieving removal efficiencies of 24% for Cr, 19% for Ni, and 17% for Zn, showing the ability to phytostabilize chromium and the higher resistance concerning the toxicity threshold. Haplopappus foliosus and Lycium chilense presented a slight tendency to stabilize chromium. Only Solidago chilensis showed little ability to extract Zn.

Photophysical and Photoelectrochemical Properties of CsPbBr3 Films Grown by Electrochemically Assisted Deposition.

Perovskite have had a great impact on the solid-state physics world in the last decade not only achieving great success in photovoltaics but, more recently, also in the implementation of other optoelectronic devices. One of the main obstacles for the adoption of Pb-based perovskite technologies are the high amounts of Pb needed in the conventional preparation methods. Here we present for the first time a detailed analysis of the photophysical and photoelectrochemical properties of CsPbBr3 films directly grown on fluorine-doped tin oxide (FTO) coated glass through a novel technique based in the electrodeposition of PbO2 as CsPbBr3 precursor. This technique allows to save up to 90 % of the Pb used compared to traditional methods and can be scalable compared with the commonly used spin-coating process. The low temperature analysis of their photoluminescence spectra, performed in both steady state and time dependence, revealed a strong interaction between electrons and longitudinal optical (LO) phonons dominant at high temperatures. On the other hand, the electrochemical and photoelectrochemical analysis proves that CsPbBr3 prepared using this new method has state-of-the-art features, showing a p-type behavior under depletion regime. This is also confirmed by photoelectrochemical measurements using p-benzoquinone as target molecule. These results prove that the proposed method can be used to produce excellent CsPbBr3 films, saving much of the lead waste.

An Assessment of the Metal Removal Capability of Endemic Chilean Species.

In Chile, there are several abandoned mine tailing impoundments near population centers that need to be remediated. In this study, the ability of Oxalis gigantea, Cistanthe grandiflora, and Puya berteroniana to remove Zn, Ni, and Cr from mine tailings was evaluated. The plants' removal efficiency, bioconcentration, and translocation factors regarding these metals were determined to assess the ability of certain endemic species from Northern and Central Chile to extract or stabilize metals. After a period of seven months, the chemical analysis of plants and tailings, together with the statistical treatment of data, indicated the inability of all the species to translocate Ni, Cr, or Zn with a translocation factor lower than one. The results showed the stabilizing character of Oxalis gigantea, Puya berteroniana, and Cistanthe grandiflora for Zn, with a bioconcentration factor close to 1.2 in all cases, and the same ability of the latter two species for Cr, with a bioconcentration factor of 1.5 in the case of Cistanthe grandiflora and 1.7 for Puya berteroniana. Finally, a removal efficiency of 9.3% was obtained with Cistanthe grandiflora for Cr and 15% for Ni; values lower than 6.4% were obtained for Zn in all cases. Improvements in the process should be sought to enhance the performance of these species for the accumulation of the target metals.

Copper Analysis by Two Different Procedures of Sequential Extraction after Electrodialytic Remediation of Mine Tailings.

The analysis of Cu distribution in pre-treated mine tailings after electrodialytic remediation was carried out by using two methods of sequential extraction. The initial content of copper in the tailings was 1109 mg Cu/kg of dry tailing, where close to 40% of the sample in weight corresponded to a soluble fraction. The tailing was treated with a leaching solution for 24 h. Three different solutions were tested: H2SO4 + HNO3 with pH = 1.9; H2SO4 + HNO3 with pH = 4.2; and NH4Cl 0.8 mol/L with pH = 5.5. After that, electrodialytic remediation experiments were carried out using an electric field of 2.7 V/cm for 15 days. The best performance for the complete cell was obtained with H2SO4 + HNO3 solutions, with a copper removal efficiency in the range of 62% to 67% and a current efficiency between 6% and 9%. The results of the remaining copper concentration between anode and cathode, from both procedures of sequential extraction, showed similar trends. The differences were mainly attributed to the use of different extractant solutions and extraction times. Soluble and exchangeable fractions were easily removed, with efficiencies higher than 80%. The lowest copper removal efficiency was obtained with NH4Cl 0.8 mol/L.

Application of a Sequential Extraction Method for Analyzing Cu Distribution in Pre-Treated Mine Tailings after Electrodialytic Remediation.

Mine tailings have been analyzed by a sequential extraction procedure after their pre-treatment with a leaching solution for 24 h and electrodialytic remediation during 15 days with a constant electric field of 2.7 V cm-1. Four leaching solutions were tested: H2SO4 + HNO3 (2:1 vol.) pH = 1.9; H2SO4 + HNO3 (2:1 vol) pH = 4.2; NH4Cl 0.8M, pH = 5.5 and 30% H2O2 adjusted to pH 2 with HNO3 1M + HCl 1M. After the treatment, the tailings were divided in six slices from anode to cathode. The highest removal efficiency of copper was obtained with H2SO4 + HNO3 pH = 1.9, which allows one to remove 67% of the copper in the total cell and 85% of the copper in the slice closest to anode. The same solution with pH = 4.2 allows one to remove 62% of the total copper. The analysis realized by the sequential extraction method indicates the easy removal of water-soluble and exchangeable fractions in all experiments, moreover, residual and sulfide are the less mobile fractions. The general trend was the movement of copper associated to different fractions from anode to cathode and its accumulation closest to the cathode in the case of exchangeable, Fe-Mn oxides and acid soluble fractions, possibly due to some precipitation of copper compounds associated with less acidic conditions.

Selenium removal from petroleum refinery wastewater using an electrocoagulation technique.

In the present work, an electrocoagulation technique was tested as a possible technological alternative for the treatment of selenium in wastewater from a petroleum refinery. For this purpose, a batch airlift reactor with air stirring was used. The sacrificial electrodes were made of iron to generate the necessary ferrous ions for the process. The results indicated a selenium removal of 90% from the wastewater after 6 h of treatment, achieving a decrease in concentration from 0.30 mg L-1 to 0.03 mg L-1. The current density was found to be an important variable for the process. In conclusion, the electrocoagulation process seems to be a feasible selenium removal technique applied to petroleum refinery wastewater.