Synthetic wastewaters treatment by electrocoagulation to remove silver nanoparticles produced by different routes

Electrocoagulation applied for textile wastewater oxidation using iron slag as electrodes

The indigo blue dye is widely used in the textile industry, specifically in jeans dyeing, the effluents of which, rich in organic pollutants with recalcitrant characteristics, end up causing several environmental impacts, requiring efficient treatments. Several pieces of research have been conducted in search of effective treatment methods, among which is electrocoagulation. This treatment consists of an electrochemical process that generates its own coagulant by applying an electric current on metallic electrodes, bypassing the use of other chemical products. The purpose of this study was to evaluate the potential use of iron slag in the electrocoagulation of a synthetic effluent containing commercial indigo blue dye and the effluent from a textile factory. The quantified parameters were color, turbidity, pH, electrical conductivity, sludge generation, phenol removal, chemical oxygen demand (COD), and total organic carbon (TOC). The electrocoagulation treatment presented a good efficiency in removing the analyzed parameters, obtaining average removal in the synthetic effluent of 85% of color and 100% of phenol after 25 min of electrolysis. For the effluent from the textile factory, average reductions of 80% of color reaching 177.54 mg Pt CoL^-1, 91% of turbidity reaching 93.83 NTU (nephelometric turbidity unit), 100% of phenol, 55% of COD with a final concentration of 298.8 mg O₂ L^-1, and 73% of TOC with a final concentration of 56.21 mg L^-1, in 60 min of electrolysis. The reduced time for removal of color and phenolic compounds in synthetic effluent demonstrates the complexity of treating the real effluent since to obtain removals of the same order a 60-min period of electrolysis was necessary. The results obtained demonstrate the potential of using iron slag as an electrode in the electrocoagulation process in order to reuse industrial waste and reduce costs in the treatment and disposal of solid waste. Thus, the slag can be seen as an alternative material to be used in electrocoagulation processes for the treatment of effluents from the textile industry under the experimental conditions presented, its only limitation being the fact that it is a waste and therefore does not have a standardization in the amounts of iron present in the alternative electrodes.

Recent trends in removal and recovery of heavy metals from wastewater by electrochemical technologies

Heavy metal-laden water and wastewater pose a threat to biodiversity, including human health. Contaminated wastewater can be treated with several separation and purification methods. Among them, electrochemical treatment is a notable clean technology, versatile and environmentally compatible for the removal and recovery of inorganic pollutants from water and wastewater. Electrochemical technology provides solution for the recovery of metals in their most valuable state. This paper analyses the most recent electrochemical approaches for the removal and recovery of metal ions. Various current works involving cell design and electrode development were addressed in distinguished electrochemical processes, namely, electrodeposition, electrocoagulation, electroflotation, and electrosorption. Cathodic reduction of metal ions has been proven in result to metal deposit on the metal, metal oxide, stainless steel, and graphite electrode. However, little progress has been made toward electrode modification, particularly the cathode for the purpose of cathodic reduction and deposition. Meanwhile, emerging advanced materials, such as ionic liquids, have been presented to be prominent to the technological advancement of electrode modifications. It has been projected that by integrating different priorities into the design approach for electrochemical reactors and recent electrode developments, several insights can be obtained that will contribute toward the enhancement of the electrochemical process performance for the effective removal and recovery of heavy metals from water and wastewater in the near future.

Removal of copper from water using a thermally regenerative electrodeposition battery

A thermally regenerative ammonia battery (TRAB) recently developed for electricity generation using waste heat was adapted and used here as a treatment process for solutions containing high concentrations of copper ions. Copper removal reached a maximum of 77% at an initial copper concentration (C_i) of 0.05M, with a maximum power density (P) of 31Wm^-2-electrode area. Lowering the initial copper concentration decreased the percentage of copper removal from 51% (C_i=0.01M, P=13Wm^-2) to 2% (C_i=0.002M, P=2Wm^-2). Although the final solution may require additional treatment, the adapted TRAB process removed much of the copper while producing electrical power that could be used in later treatment stages. These results show that the adapted TRAB can be a promising technology for removing copper ions and producing electricity by using waste heat as a highly available and free source of energy at many industrial sites.

Selective recovery of Ag(I) coordination anion from simulate nickel electrolyte using corn stalk based adsorbent modified by ammonia-thiosemicarbazide

In nickel electrolyte, Ag(I) was present at trace level concentration (10-20 mg L(-1)) and existed in the form of AgCli(1-i) coordination anion, instead of Ag(+) positive ion usually in several sources. In the present study, TSC-NH3-OCS adsorbent based on natural corn stalk modified by ammonia (NH3)-thiosemicarbazide (TSC) was synthesized and characterized using some instrumental techniques. The TSC-NH3-OCS adsorbent could selectively adsorb Ag(I) as AgCl(i)(1-i) coordination anion from the Ag(I)-Cu(II)-Ni(II) simulate nickel electrolyte, especially in the case of the very high levels of Cu(II) and Ni(II), which significantly outperforms the commercial available resins. The adsorption mechanism was believed to be electrostatic interaction of the protonated bands of AgCl4(3-) with protonated thiol form of the thioamide units by FTIR and XPS analysis. The maximum adsorption capacity in the Ag(I) single and Ag(I)-Cu(II)-Ni(II) ternary system were obtained and calculated as 153.54 and 46.69 mg g(-1), respectively. The reasons that the maximum adsorption capacity of AgCl(i)(1-i) from the single and ternary system varied widely could be explained by adsorption kinetic and thermodynamic results. In addition, three successive sorption/desorption cycle runs from ternary system were performed which indicated that the TSC-NH3-OCS adsorbent has a good performance for recovery Ag(I) from simulate nickel electrolyte.