In this research, the capability of Henna adsorbent was studied in order to remove the ions Cu(II) and Ni(II). Response surface method and central composite design were used to minimize number of experiments (21 runs) and optimize the effective parameters. The parameters were pH (2–6) for Cu(II) and (2–9) for Ni(II), initial solution concentration (10–100 mg/l), adsorbent dosage (0.1–1 g), and process time (20–150 min). It was concluded that Cu(II) removal increased from 1.8% to 73% by increasing the pH from 2 to 5.2 (maximum adsorption was at pH 5.2). Furthermore, Ni(II) removal increased from 61% to 82% by increasing the pH from 3.75 to 7.25. Maximum adsorption was obtained at pH 7.25 for Ni(II). The Cu(II) and Ni(II) removal were decreased by the initial solutions concentration enhancement. A perfect correlation (with R2 = 0.9988) between the statistical model and experiment was found for Cu(II) removal (as an example) from aqueous solution using Henna. The Langmuir and Freundlich isotherm models were also applied as adsorption mechanism. A good agreement (with R2 = 0.9945) between the Langmuir model and experimental data was investigated however Freundlich model confirmed that Henna is a proper adsorbent in Cu(II) adsorption process.
