Simple Method for Removing Lead Ion Using Orange Juice Residue

Abstract
An adsorption gel for lead (II) ion was prepared by milling still wet manclarin orange residue just after juicing with some calcium hydroxide. A previous experimen had shown that pectic acid which is present in orange juice residue gives rise to a very stable complex with lead (II) ion. The effects of the amount of added calcium hydroxide, the ratio of the weight of the adsorption gel to the volume of aqueous solution containing lead ions, contact time and pH of the aqueous solution were examined. The adsorption behavior of dry orange juice residue powder that has been prepared by drying the wet residue with lime at high temperature using a rotary kiln, a product commonly as cattle feed, was also examined and compared with the gel prepared in the present work. The following results were obtained.
(1) Nearly perfect removal of lead was achieved over the wide pH range of 4~7 by using the gel prepared from wet orange juice residue.
(2) The removal of lead decreased greatly when the gel was used with aqueous solution of a pH greater than 8 or when using a gel prepared with too much calcium hydroxide.
(3) The dry orange juice residue powder was found to be not very effective for the removal of lead because the adsorption of lead was much lower at low solid/liquid ratios.
Although the gel prepared from wet orange juice residue was found to be very effective for the removal of lead, it suffers from a degradation problem and, consequently, it seems to be difficult to preserve. The dry orange juice residue powder, however, is free from this problem. A new adsorption gel with high efficiency for lead removal and free from the degradation problem needs to be developed from orange juice residue in the future.

Key words: orange juice residue, lead (II) ion, adsorption, removal, pectic acid