Adsorption Characteristics of Hg (II) on Wood Charcoal

To make effective use of waste wood resources from thinning and waste wood, the possibility of a mercury (II) adsorbent has been studied of applying wood charcoal from sugi (Cryptomeria japonica D. Don) and hinoki (Chamaecyparis obtusa). In acid solution, the mercury (II) adsorbent characteristics of sugi and hinoki samples carbonized at temperature range of 400 to 1100°C showed selectivity, depending on the carbonization temperature and kind of wood. As far as the present study is concerned, the sample of sugi carbonized at 800°C was the highest in amount of adsorbed mercury (II), showing a higher adsorbent capacity than commercial activated carbon. The amount of adsorbed mercury (II) by a sugi sample carbonized at 800°C increased linearly up to some 65 mg/g. Then, the adsorbent capacity approached a saturation point. The threshold value was some 68 mg/g when the concentration of mercury (II) was 120 mg/l. On the other hand, activated carbon mercury (II) adsorbent amount reached some 14 mg/g and the threshold value was about 17 mg/g. The saturation adsorbent amount of the charcoal of sugi was 68 mg/g-four times as high as that of commercial activated carbon. Sugi carbonized at 800°C is much higher than the commercial activated carbon in the mercury (II) adsorbent amount per unit surface area. This showed that the charcoal of sugi is a material with a high mercury (II) adsorbent rate per unit surface area. At a carbonization temperature of 800°C, where the basic surface oxides are highest, both sugi and hinoki showed the highest mercury (II) adsorbent power. For this reason, it is considered that the basic surface oxide contributes in some way to improving adsorbent performance. With regard to the effect on the mercury (II) ab-sorbent capacity of wood charcoal, it is considered that the contents of the basic surface oxides are more significant than the alkali elution from the wood charcoal, or the surface area of wood charcoal.