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54 I-CONNECT007 MAGAZINE I MARCH 2026 commercially available ion-exchange resin, leaving space for expansion. The selected resin favored copper adsorption at a low pH, making it suitable for an acidic etchant. A pump circulated liquids through the column. During adsorption, effluent etchant was collected separately; during desorp- tion, effluent acid was recycled to the feed tank. An air purge removed residual liquids between tests, and pH and temperature were monitored at the column outlet. The test rig was used to evaluate five different flow rates. Samples were collected as instanta- neous effluent and as bulk composite volumes. Flow rates were determined volumetrically. Ad- sorption samples were analyzed for copper, chlo- ride, pH, oxidation-reduction potential (ORP), and specific gravity. Desorption samples were analyzed for copper, chloride, free acid, sulfuric acid, pH, and specific gravity. Because residual rinse water diluted the initial effluent, the first portion of liquid from each run was discarded and measured as waste. This was a significant issue that had to be considered and solved before we could scale up the equipment. Adsorption results showed consistent trends. Copper breakthrough curves followed the same shape across tests, differing mainly in time to breakthrough (when effluent copper equaled feed concentration). Chloride concentration dipped slightly at the start, then returned to near-feed lev- els. As copper was removed and protons released, effluent pH increased significantly, as expected. ORP initially spiked in most tests, suggesting that the resin preferentially adsorbed Cu + over Cu² + , then stabilized at near-feed conditions. Specific gravity decreased during copper removal, reflect- ing reduced dissolved copper concentration, then approached feed values. Temperature measure- ments showed slight cooling during adsorption. Copper concentration data fit well to an empiri- cal model relating concentration to time, and efflu- ent pH decline after peak values followed a linear relationship. Using fitted equations, the amount of copper removable from various bulk volumes of etchant was predicted. Results showed that copper removal depends on both the number of bed volumes (BV) processed and the specific inlet mass flow rate of copper. Larger columns pro- cess fewer bed volumes per unit etchant volume, increasing the total copper removed. Once the Figure 2: Test setup in reality.