酸性甲醛改性对花生壳吸附重金属离子的影响

Effects of acidic formaldehyde treatment of peanut hull on its adsorptive capacities for heavy metals

花生壳的酸性甲醛改性对重金属离子的吸附有较大影响。改性过程使花生壳中一些含有羟基、羧基、芳香环、C—O和C—O—C键的混合物被脱除。改性后花生壳的等电点略有升高,而和羧基有关的表面负电荷量则明显降低。混合物的脱除使Pb2+的吸附量明显降低,Cr3+、Cu2+的吸附量改变不大。改性使羧基减少的同时也暴露了新的Cr3+、Cu2+的吸附位点。改性还有利于增加重金属离子在花生壳内孔中的传质速率,从而使吸附达到平衡的时间略有减少。

Modification of peanut hull by treatment with formaldehyde in acidic medium was effective for remo ving most of its color ingredients, The treatment caused a small increase in the point of zero charge of the surface resulting in a significantly reduced negative surface charge; the peanut bull＇s capacity for Pb^2＋ was reduced notably while the capacities for Cu^2＋ and Cr^3＋ were also reduced but to smaller degrees. The treatment removed the carboxyl and other organic groups on the surface making more sites available for adsorption and thus enhanced diffusion of heavy metal ions in internal pores of the modified peanut hull,