Behavior of Reduction Precipitation of Nickel Adsorbed on the Surface of Sulfur-Impregnated Carbonaceous Cotton

In this study, reduction treatment was applied to nickel adsorbed on a sulfur-impregnated carbonaceous cotton prepared using sulfide aqueous solutions, and the precipitation behavior of nickel was determined. Two types of sulfide solutions, K2S and Na2S, were used for preparation of the sulfur-impregnated adsorbent. A cotton immersed in sulfide solution was pyrolyzed in an electric tubular furnace to obtain the fibrous adsorbent. Nickel was adsorbed on the surface of the adsorbent by passing a 10 mM Ni(NO3)2 solution through the obtained adsorbent, and the fibrous adsorbent adsorbed nickel was heated in N2 atmosphere using an electric tubular furnace as reduction treatment. The adsorbents on each process were analyzed by X-ray diffraction (XRD) and observed by scanning electron microscope (SEM), respectively, and the effects of sulfide type, concentration and reduction temperature on the precipitation behavior of nickel adsorbed on the sulfur-impregnated cotton was examined. The adsorption amount of the adsorbent obtained using 1.0 M Na2S was higher than that using 1.0 M K2S. From the analysis of adsorption isotherms using Langmuir and Freundlich model, the Langmuir model matched the data better than the Freundlich model for both adsorbents, and maximum adsorption capacity calculated from the Langmuir isotherm model for the adsorbent obtained using Na2S was 0.43 mmol/g, which was higher than that using K2S (0.27 mmol/g). Ni3S2 was precipitated on the adsorbent prepared using 1.0 M K2S by reduction treatment at more than 800 oC, while metallic nickel was precipitated on the adsorbent prepared using 0.5 M Na2S by reduction treatment at more than 800 oC. The amount and size of the precipitated particles increased with increasing the reduction temperature.