Table of Contents
Advances in Environmental Chemistry
Volume 2015, Article ID 543614, 6 pages
Research Article

Temperature Induced Aggregation and Clouding in Humic Acid Solutions

Department of Chemistry, University of Idaho, Moscow, ID 83844-2343, USA

Received 8 December 2014; Accepted 30 January 2015

Academic Editor: Claire Richard

Copyright © 2015 Leah Shaffer and Ray von Wandruszka. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Humic acids in aqueous solution demonstrate inverse temperature-solubility relationships when solution conditions are manipulated to reduce coulombic repulsion among the humic polyanions. These effects were followed by dynamic light scattering (DLS) measurements of the resulting aggregates, as well as the addition of a polarity sensitive fluorescent probe (pyrene). The humic solutions could be primed for temperature induced clouding by carefully lowering the pH to a point where hydration effects became dominant. The exact value of the cloud point (CP) was a function of both pH and humate concentration. The CPs mostly lay in the range 50–90°C, but DLS showed that temperature induced aggregation proceeded from approximately 30°C onward. Similar effects could be achieved by adding multivalent cations at concentrations below those which cause spontaneous precipitation. The declouding of clouded humate solutions could be affected by lowering the temperature combined with mechanical agitation to disentangle the humic polymers.