Electrochemical membrane reactor: In situ separation and recovery of chromic acid and metal ions

Electroplating wastes

Electroplating and other metal finishing industries, like every metal and metallurgical industry, are associated with the generation of waste. Spent electroplating baths, waste pickle liquors, etching solutions and rinse waters from electroplating units and steel finishing operations are complex solutions containing acids and several hazardous metals. It is compulsory, for environmental and economic reasons, to treat these solutions for recovering acid, metals and/or reusing these solutions/waters. This article is a review on the characterization of the wastes that are generated in electroplating industry, steel processing and copper etching in printed circuit boards manufacture, as well as on the treatment and regeneration methods of such streams. Various techniques, such as neutralization, crystallization, evaporation, pyrohydrolysis, electrodialysis, ion exchange, classical solvent extraction and membrane-based solvent extraction are presented, their advantages and disadvantages being scrutinized.

Wavelength selective separation of metal ions using electroactive ligands

Photo-induced electron transfer to an irreversibly electroactive ligand is introduced as a novel method for separating meta ions.

Novel electrodialysis cation exchange membrane prepared by 2-acrylamido-2-methylpropane sulfonic acid; heavy metal ions removal

In the present work a novel heterogeneous cation exchange membrane (CEM) composed of poly vinyl chloride (PVC) and 2-acrylamido-2-methylpropane sulfonic acid based hydrogel (AMAH) was prepared. The membranes were fabricated with different fractions of AMAH to optimize the performance in desalination. The hydrogel was characterized by FT-IR to prove the successful synthesis. The membrane properties such as permselectivity, ionic permeability, flux, water content, electrical resistance, morphology, contact angle and dimensional stability were evaluated. Modified membranes showed acceptable dimensional stabilities, more hydrophilic surface, higher water content and porosity. SEM images revealed the formation of a more porous membrane structure. Membrane permselectivity and transport number showed a relatively constant then decreasing trend in Na⁺ and Ba²⁺ solutions. The experimental results showed that the incorporation of AMAH into the PVC matrix obviously improved ionic permeability and flux of Na (∼9%) and Ba (∼23%). Membrane electrical resistance was declined about 36% by adding AMAH in the membrane structure. Membranes' performance in potassium and heavy metal ions removal showed a remarkable separation capacity of K⁺ (99.9%), Pb²⁺ (99.9%) and Ni²⁺ (96.9%). Membranes showed desirable potential for scaling removal.

Ion-exchange membranes in chemical synthesis – a review

The applicability of ion-exchange membranes (IEMs) in chemical synthesis was discussed based on the existing literature. At first, a brief description of properties and structures of commercially available ion-exchange membranes was provided. Then, the IEM-based synthesis methods reported in the literature were summarized, and areas of their application were discussed. The methods in question, namely: membrane electrolysis, electro-electrodialysis, electrodialysis metathesis, ion-substitution electrodialysis and electrodialysis with bipolar membrane, were found to be applicable for a number of organic and inorganic syntheses and acid/base production or recovery processes, which can be conducted in aqueous and non-aqueous solvents. The number and the quality of the scientific reports found indicate a great potential for IEMs in chemical synthesis.

Study and Preparation of Electrocatalytic Ceramic Membrane Electrode

The novel electrochemical membrane reactor for wastewater treatment was designed and introduced. As the key part of the electromembrane reactor, the tubular membrane electrode was prepared and researched. The tubular inorganic ceramic membrane was endowed with electroconductivity by the deposition of pyrolytic carbon from propylene by chemical vapor deposition. The electrocatalytic property of the membrane electrode was realized through dip-coating with chloroplatinic acid solution, drying and hydrogen reduction in order that the electrocatalyst of reduced platinum can be supported. The SEM characterization and water flux test of the membrane electrode show that membrane separation and electrocatalysis can be integrated together.

Concentration and purification of chromate from electroplating wastewater by two-stage electrodialysis processes

A designed two-stage electrodialysis system is proposed to concentrate and purify chromate from a low pH electroplating wastewater using monovalent selective electrodialysis membranes. With low pH of the raw water (pH 2.2) in the first stage, chromate was presented as HCrO(4)(-) and monovalent ions (HCrO(4)(-), NH(2)SO(3)(-), Na(+) and Cl(-)) were able to pass through the membrane thus chromate was concentrated up to 191%. Higher current density, flowrate and more membrane area all increased the chromium recovery. When pH was adjusted to 8.5 before entering the second stage, the chromate species was presented as divalent CrO(4)(2-) and retained in the concentrated stream, and the rest monovalent ions (NH(2)SO(3)(-), Na(+) and Cl(-)) were separated by passing through the membrane. For example, 45% of the chlorides were separated in this study. The separation efficiencies in the second stage were also increased when the current density, flowrate and membrane area were increased. Electron Spectroscopy for Chemical Analysis was used to examine the surface chromate species for stage 1, and anion exchange membrane showed more chromate fouling comparing to cation exchange membrane due to more adsorption and concentration polarization effects for the anion exchange membrane.