The reduction property of activated carbon fibers (ACFs) enables them to be used in the recovery of noble metals from wastewater, or in the extraction of gold or silver from ore leaching solutions. In order to effectively recover or extract noble metals, it is important to enhance the reduction capacity of ACFs and to improve the particle size of the noble metal reduced and adsorbed on the surface of activated carbon fibers. In this paper, the effect of the preparation method and surface modification of ACFs on their reduction capacity was studied. The results show that the preparation methods of ACFs have significant influence on their reduction-adsorption capacities for silver ions in solution-those ACFs prepared with phosphoric acid or zinc chloride activation have much higher reduction capacities. Moreover, surface modification of ACFs with some inorganic oxidants such as nitric acid, potassium permanganate, or hydrogen peroxide, though resulting in a small decrease of specific surface area or pore volume, will enhance the reduction capacity of oxidized ACFs for silver ions. Furthermore, methylene blue, aniline, or p-nitrophenol present in solution or adsorbed on ACFs can also significantly increase the reduction capacities of sisal-based ACFs for silver ions. (C) 2003 Elsevier Science Ltd. All rights reserved.
