CC PACKET 09251984 - Laserfiche WebLink

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The advantages of.the ion exchange treatment system are: the Activated Carbon Adsorption water savings are significant; the feedstream can be dilute as is the case in rinse waters; and the energy consumption is low. The plating baths in electroplating and printed circuit board The disadvantages are: capital costs are high; chemical, labor manufacturing shops normally become contaminated with a variety and maintenance costs are high; the equipment is complex; and of substances. The important contaminants of concern to the the performance of the system depends on the operator. proposed metals recovery system are those that adversely affect the ion exchange resins. These important contaminants include strong oxidants that may physically break down the resin, Electrolytic Recovery chelating agents and oils or other organics that may gradually k foul the resin and various suspended solids that may foul the This is a process in which there is an electrochemical i ion exchange column. reduction of metal ions to elemental metal. In the electrochemical cell a sufficient level of direct current Therefore, it is essential that these organic contaminants be voltage is applied across two electrodes, overcoming the removed from the waste water prior to the ion exchange reversible electromotive force of the cell, causing the metal treatment in order to preserve the longevity of the resins. ions to plate out at the cathode. The cathode is the electrode Activated carbon performs this required step by the process of at which electrons are taken up by the metal and reduction adsorption. occurs. The other electrode is the anode. Oxidation occurs here and electrons are given up to the electrode. There are three important steps in the process of adsorption of dissolved organics in the waste water by the granular activated The electrolytic recovery of metals has been proven technically carbon. First is the transport of the solute through a film on feasible by the primary and secondary copper industry. Copper the surface of the activated carbon granule to the exterior is purified using these electrochemical techniques. surface of the carbon. The second step is the diffusion of the Electrolytic recovery is also used to recover tin, silver, solute through the pores of the carbon to its interior. copper and other metals from plating and etching drag out Finally, adsorption of the solute occurs on the interior wastes in some electroplating plants. surfaces of the pore and capillary spaces of the activated carbon. Electrolytic recovery was chosen as the metal recovery process for the copper and cadmium wastes entering the Facility. The effectiveness of adsorption by activated carbon is Copper will be recovered using a large electrowinning tank dependent upon a number of factors. The physical and chemical while cadmium recovery will require a smaller plating cell. nature of the solution, the nature of the material to be adsorped, including its molecular size and polarity, the type Zinc and nickel waste streams are believed to be contaminated of contacting system (carbon column for example) and its mode with copper and other metals along with other impurities. The of operation, and the nature of the carbon itself. electromotive series position of nickel and zinc are higher than the contaminating metals so their recovery by this Activated carbon canisters would be used at the industrial electrolytic process is uneconomical. shops as a prefilter to the ion exchange system. At the Facility there will be two activated carbon columns installed The important factors which determine the efficiency of in series. At the Facility the main function of the carbon electrolytic recovery of metals are, water temperature, water would be to trap suspended solids and remove organics from flow rate, the current density and electrode area of the cell nickel and copper waste waters which arrive at the facility in (for plating), the type of metal and metal concentration in the bulk shipments. water, and the types of contaminants and their concentration in the water. Once the carbon columns have reached their capacity they must be replaced with fresh activated carbon columns. In order to There is also a possibility of reusing the spent electrolytic be disposed of they will first be dried and then incinerated. solutions as a regenerant solution for the ion exchange resins. The ash may then be disposed of in a sanitary landfill. Since no heavy metals are adsorped by the carbon, none will be present in the ash. A-4 A-5