Rice husk treated by sodium hydroxide had a potential to be an inexpensive adsorbent for recovery of nickel from electroplating industry. NaOH-treated rice husk could be used in many forms of grain such as no g-ound (RHG-T), powder < 75 μm (RH75-T) and heated at 500°C (RH500-T). The maximum adsorption capacity of RHG-T, RH75-T and RH500-T were 4.27, 5.29 and 3.88 mg g~(-1), respectively. Nickel adsorbed onto NaOH-treated rice husk was also completely eluted by 0.025 M H2SO4. In addition, the ratio of Ni and Na interchange and elution test indicated that the mechanism of nickel adsorption by NaOH-treated rice husk was ion exchange process. The average ratios of Ni:Na for nickel adsorption by RH75-T, RHG-T and RH500-T were 1:1.5, 1:2 and 1:1, respectively. The finctional groups of -CH2OH, silanol (-Si-O-H) and siloxane (SiO-Si) were transformed by NaOH treatment to -CH_2O~-Na~+, -Si-O'Na~+ and [Si-O-Si]~-Na+. SEM/EDX, FTIR spectrum and the nickel adsorption by NaOH-treated avaicel (AV-T) and NaOH-treated silicic acid (SA-T) indicated that RH75-T could use both -CH_2OTMa~+ and -Si-O~-Na~+ to adsorb nickel, while RHG-T and RH500-T trended to occur by -CH_2O~-Na~+ and -Si-O~-Na~+, respectively.
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