EFFECTS OF GEL PROCESSING ON THE PROPERTIES OF HUMIC-ACID ISOLATED FROM THE ALGA PILAYELLA-LITTORALIS - A HUMIC-ACID AEROGEL

Humic acid in the live alga Pilayella littoralis was isolated as an aq ueous gel by a standard sequential extraction method augmented with re moval of alginic acid. Portions of the aqueous gel were (1) vacuum ove n dried at 40 degrees C, (2) freeze dried after cooling in liquid N-2, and (3) dried with supercritical fluid CO2 after substitution of wate r in the gel with acetone. This paper compares the analytical and spec tral properties of the products with compost derived HA and reports si gnificant differences in their surface areas, packing densities, water retention, solute sorption and metal binding properties. The results are discussed in terms of different product morphologies determined by scanning electron microscopy. The aerogel obtained by supercritical f luid CO2 drying of an HA gel from Pilayella has the highest surface ar ea (188 m(2) g(-1)) reported for a humic acid.