THE REMCO METAL RECOVERY ION EXCHANGE (MRIX) PROCESS

The Remco Metal Recovery Ion Exchange (MRIX) process is unique in that all of our skid mounted systems are complete water treatment units featuring microprocessor control, very low water use, complete prefiltration and VERY efficient regenerant usage. We will describe the metal recovery ion exchange process in detail starting with your feed to the system (you can pump or we can pull using a Remco Engineering Sumpless Pump). The Metal Recovery Process Rinse water is collected from your process and held in the main buffer tank which is included with all systems. This tank is sized for 20-60 minute retention. It serves as a buffer when the flow exceeds the design flow rate and also allows service or maintenance without interrupting production. Here the waste stream is pH adjusted to the optimum required by the ion exchange resin. The water is then transferred through a media pre-filter where sediment is removed. This transfer is accomplished with a two stage level controller that is interfaced with the pH controller. In operation the tank must be at the upper level control point and at the correct pH before the system goes on line (pumps through columns). The system stays on line until the tank reaches a second (lower) level indicator. This mechanism assures us of always having a buffering action that accommodates a varying incoming pH while delivering a very stable pH to the ion exchange resin columns. Our system utilizes duplex feed pumps, reserving one pump for standby operation. With this arrangement, down time is kept at a minimum. The media filter is a column of sand like material (Aluminum silicate) that works as a depth filter. The more it is run, the finer it filters. When flow drops below the design flow rate, the filter is backwashed into a bag filter with the separated liquid being returned to the buffer tank. The contents of this sediment is entirely dependent on what debris may be going down the drains. Any dissolved metal contained in the liquid portion of the backwash is pH adjusted and processed back through the system. NOTHING GOES TO DRAIN WITHOUT PASSING THROUGH THE COLUMNS. From the media filter the filtered metal bearing water is directed through the top of the first column of ion exchange resin out the bottom and into the top of the second column. From here it is discharged to the sewer. This configuration is referred to as lead/lag. Their respective positions to the flow of the rinse waters changes during the regeneration operation. It is in these columns where the metal ions are exchanged and captured on the exchange sites of the resin. The ion exchange resin used varies with the application but for this example we use a weak acid chelated resin, used for Copper, Nickel, and Lead recovery. This resin is used in the sodium form. A metal ion is exchanged for a sodium ion in a similar fashion to a home water softener. For example, a Copper ion is captured when it passes through the column and is exchanged for two Sodium This is because the chemical valence of Copper is 2, Sodium 1, therefore, 1 Copper = 2 Sodium when exchanged. As you can see, we are not de-ionizing (DI) the water but exchanging one ion (ion exchange) for another. The advantage of this process is that you only capture what you need to remove from solution and not what you are permitted to let pass. As the ion exchange exchange process continues, the resin slowly fills up with metal. The point at which regeneration is required is determined by monitoring the stream after is has passed through the lead (first) column and before is reaches the lag (second) column. Rising metal levels here indicate the lead column is exhausted and requires regeneration. The operator pushes a button which initiates the microprocessor to begin the regeneration cycle. The complete cycle is simple to describe, but involves a number of valves, timed cycles, and switching. Rather than depend on manual operation and the possibility of error, a microprocessor assures you of proper functioning and very low levels of metal in the effluent. When the regeneration cycle is initiated, the lead column is taken off line while the following (lag) column with its available exchange sites is maintained on line to process the wastewater. The lead column is then reverse rinsed from bottom to top with water. The water is returned to the the holding/pH adjust tank. Next, the column is backwashed with of 8-15 % acid solution. The acid backwash supplies hydrogen ions which exchange with the metal ions on the resin. The resin cannot hold on to the metals at low pH. The metal ions and the acid are returned to the acid holding tank as metal salt. This is approximately 10 gallons of solution per cubic foot of resin. The column is then rinsed with fresh water with the rinse diverted to the head of the system as it contains some metal and will require pH adjustment and polishing for metal removal. After the thorough fresh water rinse, a solution of 5% sodium hydroxide is passed through the column. This replaces the hydrogen ions on the resin with Sodium.and prepares the column for operation. If the column were left in the hydrogen form, every time a metal ion came by, it would be exchanged for the Hydrogen ion. This would lower the pH locally and cause another metal ion to be released, this would cause the metal to pass through the column (not good). The column is backwashed again to remove the excess caustic and this rinse water, as with the others, is diverted to the head of the system for reprocessing. The entire regeneration cycle takes about 3-5 hours depending on the system size and customer requirements. The regenerated column is placed back on line in the lag position. The column that was previously second is now lead. The clean column is always second in line. By testing and regenerating when levels rise between the columns we are always assured of very low metal concentration in the effluent because the waste stream still has to pass through a column with available exchange sites. There are several methods for recovering the metal from the regenerant solution. One is to collect the metal as a salt by evaporation. Some salts such as the Sodium forms of Cyanide and Chromium or the Sulfate or Chloride salts of Copper and Nickel have a slight value which allow for reclamation at minimal costs.