Waste, removal electrochemical processes

BDD electrodes are commonly used for electrochemical (waste) water treatment because of their efficient ability for total organic carbon (TOC) removal. The aim to carry out selective electrochemical processes seems therefore to be self-contradictorily. 

Electrolytic treatment technologies have definite advantages over these more common treatment processes. The primary benefit is that chemical change in an electrochemical process is brought about by the ability to add or remove electrons from species to be treated. This eliminates the use of redox agents to treat wastes and also removes the need to treat spent redox streams. Other, equally important, benefits of electrochemical processes include close control of reactions through control of the applied potential or current lower operating temperatures and hence lower costs increased possibility of on-site treatment, especially in small-scale use possible simultaneous use of the anode and cathode for waste minimization and the ability to... 

Kleifges, K.H., G. Kreysa, and K. Juttner (1997). An indirect electrochemical process for the removal of NO c from industrial waste gases. J. Appl. Electrochem. 27, 1012-1020. 

The environmental importance of the removal of gaseous pollutants from flue and waste gases has led to development of more efficient processes. Therefore a number of electrochemical processes which do not necessitate the continuous use of chemical reagents, which is the main problem besides the generation of huge amount of waste in some traditional FGD processes, have been proposed and most of them have been included in this text [1],... 

Many electroless coppers also have extended process Hves. Bailout, the process solution that is removed and periodically replaced by Hquid replenishment solution, must still be treated. Better waste treatment processes mean that removal of the copper from electroless copper complexes is easier. Methods have been developed to eliminate formaldehyde in wastewater, using hydrogen peroxide (qv) or other chemicals, or by electrochemical methods. Ion exchange (qv) and electro dialysis methods are available for bath life extension and waste minimi2ation of electroless nickel plating baths (see... 

The first equation is an example of hydrolysis and is commonly referred to as chemical precipitation. The separation is effective because of the differences in solubiUty products of the copper(II) and iron(III) hydroxides. The second equation is known as reductive precipitation and is an example of an electrochemical reaction. The use of more electropositive metals to effect reductive precipitation is known as cementation. Precipitation is used to separate impurities from a metal in solution such as iron from copper (eq. 1), or it can be used to remove the primary metal, copper, from solution (eq. 2). Precipitation is commonly practiced for the separation of small quantities of metals from large volumes of water, such as from industrial waste processes. 

Andco Environmental Processes, Inc., has developed an electrochemical iron generation process to remove hexavalent chromium and other metals from gronndwater and aqneons wastes. As contaminated water flows through a treatment cell, electrical cnrrent passes between electrodes, releasing ferrons and hydroxyl ions. The small gap between electrodes allows almost instantaneons rednction of chromium ions. Depending on the pH, varions solids may form. 

Electrochemical iron generation is a site-specific technology that is pH dependent. Process pH should be from 6 to 9. Optimal removal efficiencies require electrochemical treatment in combination with an ideal precipitation pH for the metals being removed. Nearly all fuU-scale systems include a pH control system. Andco performs lab and pilot-scale testing to evaluate the ability of the process to treat a particular waste stream. If flow rates or contaminant loads fluctuate, control equipment is required to compensate for changes in influent. 

As discussed, the aqueous waste with hexavalent chromium requires reduction of chromium to the trivalent state prior to metal removal because hexavalent chromium does not form a precipitate. Demonstrated reducing agents are sodium metabisulfite (Na2S205), sulfur dioxide (S02), ferrous sulfide (FeS), and other ferrous ion (ferrous sulfate, ferrous chloride, or electrochemically generated ferrous ion). The treatment processes using these are described below. 

Finally, soil remediation processes are farther along than the remediation of low-level waste because some practical tests have been made in the field. In some systems, the results are those desired. The costs of the thermal process for removing metal from soils are so high that funding of the development of the electrochemical approach would seem to offer good returns. 

However, such a complex system would not be helpful to describe organic-removal wastewater-treatment processes because of its high degree of complexity and, therefore, in an attempt to achieve a useful model, some assumptions could be made in order to simplify the model. Hence the transformation of this distributed-parameter model in a simpler lumped-parameter model is very common in the modeling of wastewater-treatment processes, because it is not very important to obtain detailed information about what happens in every point of the cell but simply to know in a very simple way how the pollution of a influent waste decreases at the outlet of the electrochemical cell. In this context, there are three types of approaches typically used ... 

ERIX [Electrochemically Regenerated Ion exchange system] A process for removing hydrofluoric acid from aqueous wastes from the electronics industry. The fluoride ion is trapped in an ion-exchange resin, which is continuously regenerated electrochemically. Developed by BOC Edwards and first installed in the University at Albany, State University of New York, in 2006. 

Mercury salts have been known for a long time to be toxic to human health. This problem has been stressed during the two past decades, leading various countries to develop research programs aimed to remove mercury salts from industrial waste water. Available methods are either chemical, involving ion exchange resins and various oxidation or reduction processes, or physical, using ultrafiltration techniques, evaporation of solutions or electrochemical treatments. 

Cryolite is utilized in the manufacture of aluminum, in the processing of aluminum waste (as a flux in the electrochemical removal of magnesium), as a flux in the aluminization of steel and in welding technology, in the manufacture of glass and enamel, as an additive in the manufacture of abrasives and as an auxiliary product in the remelting of light metals. 

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