Thread Content
Taking the recovery of cobalt and manganese through continuous ion exchange as an example, the operation process of a continuous ion exchange system consists of the following steps: (a) Operation of the adsorption bed – The water fed for continuous ion exchange is stored in a feed tank; once certain feeding conditions are met, it is pumped into the continuous ion exchange moving bed using a feed pump. Feeding is carried out in reverse direction, and the feed flow rate is controlled by adjusting the frequency of the feed pump； As the wastewater passes through the continuous ion-exchange closed-bed moving-bed resin, the cobalt and manganese ions in the wastewater are selectively adsorbed by the resin. Depending on the flow direction of the feed, the resin at the bottom of the continuous ion-exchange closed-bed moving bed becomes saturated first, while the fresh resin at the top ensures that the concentration of cobalt and manganese ions in the effluent remains very low, thereby improving the recovery rate of cobalt catalysts and ensuring the quality of the effluent. ð After the resin transfer operation has proceeded for a certain period of time, and when the saturated resin at the bottom needs to be regenerated, the continuous ion exchange inlet valve and outlet valve are closed, and the resin transfer process begins. At this point, the adsorbed saturated resin is transferred, via an automatically controlled discharge valve, into the resin lift pump. Under the action of compressed air, the saturated resin moves from the resin lift pump to the resin reservoir at the top of the desorption column, and from there it enters the desorption column to await regeneration. While the saturated resin is transferred, an equal amount of freshly regenerated resin that has been fully regenerated is added from the resin reservoir at the top of the continuous elution column ； ð Resume operation: Once the saturation resin transfer is complete, close the resin transfer inlet and outlet valves, open the feed and discharge valves, and resume normal operation; the continuous exchange flow rate is adjusted to the design value via frequency control of the feed pump. (b) Operation of the regeneration bed: Once the resin in the adsorption bed becomes saturated and is transferred to the regeneration bed, the typical regeneration steps are as follows: After the resin becomes saturated through adsorption, it contains unadsorbed cobalt-containing wastewater in its pores; this wastewater must be returned to the feed stream for re-adsorption. Since the amount of this wastewater is very small, not exceeding 4 tons, it does not dilute the cobalt concentration in the raw water. Therefore, it can be directly fed into the continuous ion exchange feed tank and mixed with the stainless steel membrane filtrate before being used for adsorption. ð To desorb the water adsorbed on the resin after washing, it is first desorbed using recycled acid; during this process, some water is pushed out from the gaps in the resin. By controlling this process, approximately 2 tons of water can be recovered for reuse. This process can be accomplished through automatic control valves. Collection begins when the desorption solution turns red; once the concentration of cobalt ions to be desorbed decreases, the acid used will also be exhausted, at which point fresh acid is used for desorption. The former part goes directly into the cobalt catalyst recovery tank for reuse, while the latter part is used for application. The resin that has been completely desorbed is rinsed with water to wash away any excess acid in it. The first portion, due to the high acid concentration, is sent directly back to the acid recycling tank, while the second portion, containing a small amount of bromide ions in the water, can be used to prepare hydrobromic acid. The resin is regenerated with acid and alkali on a regular basis according to process requirements. The resin is thoroughly regenerated using hydrochloric acid and sodium hydroxide; the regeneration process is the same as the desorption process. After regeneration, wash with water; the regeneration waste liquid and washing water are discharged ； ð The resin is completely desorbed through transfer, and then enters the resin lifter of the regeneration column; compressed air is used to transfer it from the resin sump to the sump of the dense moving-bed resin. As the saturated resin is continuously transferred for regeneration, it enters the top of the continuous regeneration dense moving bed via the discharge valve of the sump. ð Resin rinsing can affect normal operation due to factors such as contamination of the exchange medium; therefore, it is necessary to perform resin rinsing after a certain number of operating cycles. The interval between resin rinsings can be determined based on factors such as the turbidity of the incoming water, the quality of the outgoing water, the operating pressure difference, and the exchange capacity. Generally, rinsing should be carried out every 10 to 20 operating cycles. Once the resin has been regenerated in the regeneration bed, it is transferred to a rinsing tank. Water is introduced from the bottom of this tank to rinse the resin; any contaminants and broken pieces of resin can be washed away by the water flow, while the clean, intact resin is then transferred to a compact moving bed for the adsorption process ； Based on actual usage, an appropriate amount of fresh resin can be added regularly after rinsing the resin, with the amount added depending on the amount of resin that has been damaged ； ð The cobalt catalyst solution stored in the extraction tank for extraction is transported to the process locations via a chemical pump ； ð Wait until the analysis of a batch of resins is completed, then wait ； After the resin from the high-level tank of the regeneration column is transferred to the regeneration column, the next round of resin desorption (regeneration) and transfer is carried out.