Rambutan pericarp (Nephelium lappaceum L.) as bioadsorbent of cadmium in aqueous solution.

Abstract

Numerous bodies of water that provide benefits to man have been polluted nowadays due to accumulation of heavy metal wastes resulting from anthropogenic activity. Cadmium is one of those toxic metals known to create long-term detrimental effects to all animals including man. In connection to this, the ability of rambutan pericarp to remove cadmium from its aqueous solution was evaluated. The pH (3, 5, 7, 9, and 11) of the aqueous solution and the particle size of the rambutan pericarp (250 < x < 710 and 710 < x < 1180 µm) were the parameters used to determine the efficiency of the pericarp to remove cadmium. Following results of one-way ANOVA (a = 0.05), an insignificant difference (p = 0.064) was obtained from the mean removal efficiencies at varying pH values. As per two-tailed t-test, there is also statistically insignificant difference (p = 0.175) between means from smaller and larger particle sizes. Theoretically, cadmium binding greatly depends on the pH of the surrounding solution; in the case of physical binding sites on the plant cell wall, extreme pH values precipitate cadmium out of the solution, if not, compete with it by protonating free binding sites. Adsorbents in smaller sizes exhibit a larger surface area allowing the formation of more metal complexes. Nonetheless, powdered rambutan peel can still be considered a potential heavy metal biosorbent by its increasing removal efficiency with dosage. Further studies are recommended to assess its binding abilities on other heavy metals. Use of larger sample size is also suggested to yield more accurate results.