<![CDATA[Copper (Cu) in industrial effluent pollutes the environment if discharged untreated. This study optimised Cu removal using waste eggshell adsorbents and identified the governing operating factors. Chicken eggshell, a 50:50 (w/w) chicken–duck mixture, and duck eggshell were washed, dried at 110 °C, sieved to 140 mesh and calcined at 500 °C for 2 h. A complete 3 × 4 × 2 factorial experiment combined the three adsorbents with doses of 10, 20, 30 and 40 g/L and contact times of 60 and 120 min, giving 24 treatments stirred at 200 rpm. Cu was measured by flame atomic absorption spectrophotometry at 324.8 nm. Analysis of variance showed all three main effects were highly significant while no two-factor interaction was, indicating additive behaviour; adsorbent mass explained 49.8% of total variation, contact time 39.1% and adsorbent type 10.5%. Tukey tests separated all adsorbents and all doses. Optimum conditions within the design space were 40 g/L duck eggshell for 120 min, reducing Cu from 0.1940 to 0.0865 mg/L (55.41% removal). Adsorption capacity fell from 8.10 to 2.69 μg/g as dose rose, so highest removal coincided with least efficient material use. Eggshell waste is therefore a promising low-cost biosorbent for polishing Cu-bearing water.]]>
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