Characteristics of sequential, solvent pre-extraction in the isolation of humic acid from the alga Pilayella littoralis

Plants are newly discovered sources of important biopolymers called humic a cids (HA). Purified HA isolation from plants and other sources begins with sequential Soxhlet extraction with diethylether, acetone, ethanol and dioxa ne. We have investigated the characteristics of these steps in the isolatio n of HA from the brown alga Pilayella littoralis. The mass balance of the t otal HA isolation procedure and the time dependences of each step are repor ted. Experimental extraction variables included the solvent cycle time, tem perature, age since harvesting of the Pilayella source material and the len gth to diameter ratio of the source extracted. Non-humic constituent extrac tion from Pilayella does not depend on solvent diffusion in or out of the s ource matrix. Extraction rates are determined by rapid, non-ideal equilibri a or zero order kinetic processes, depending on the solvent, the duration o f extraction and the age of the Pilayella sample. The equilibria and kineti cally controlled steps have small temperature dependences. The data will as sist HA isolation from other sources. Since non-humic substances are remove d, we endorse reflux solvent Soxhlet pre-extraction in the isolation of pur ified HA from plants and other sources.