Precipitation of humic acid with divalent ions

Niels Peder Raj Andersen, Lene Haugaard Mikkelsen, Kristian Keiding

Research output: Contribution to journalJournal article

5 Citations (Scopus)


The aim of this study is to investigate precipitation proper-ties of humic acid (HA). This is done by studying a commercial available humic acid salt (HA) from which a phase diagram is established by adding various amounts of BaCl2 to different concentrations of HA at pH 5.5.
The phase diagram shows tree characteristic regions with markedly different precipitation courses: region I at HA concentration below 0.15g/l, region H at HA concentration between 0.15 and similar to2g/l and rgeion IV at HA concentration above 3.5g/l. Furthermore, a forth intermediate region M is observed between similar to2 and 3.5g/l.

In order to understand these measurements and precipitation behaviour a phase diagram model is constructed using a simple thermodynamic approach. The result of this analysis shows that precipitation in region I and U can be explained by a simple equilibrium reaction between the HA and Ba2+.

The phase diagram model can not account for the observed precipitation in region III and However, in region IV the HA appears to posses colloidal properties, which is supported by precipitation taking place at a constant zeta-potential -21mV with the same amount of added barium ion regardless HA concentration.

With respect to region III, it is not exclusively determined whether precipitation is caused by HA behaving as a polyelectrolyte or possessing colloidal properties.

The general observation throughout is that HA appears to behave as a polyelectrolyte at low concentrations and exhibits colloidal properties at high concentrations.
Original languageEnglish
JournalJournal of the Chinese Institute of Chemical Engineers
Issue number6
Pages (from-to)525-528
Number of pages4
Publication statusPublished - 2001

Cite this

Andersen, N. P. R., Mikkelsen, L. H., & Keiding, K. (2001). Precipitation of humic acid with divalent ions. Journal of the Chinese Institute of Chemical Engineers, 32(6), 525-528.