Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 8, pp. 1375−1379.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
V.V. Kotov, D.V. Nenakhov, K.E. Stekol’nikov, O.V. Peregonchaya, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82,
No. 8, pp. 1277−1281.
OF SYSTEMS AND PROCESSES
An effective procedure to isolate humic acids from the
organic substance of soils in a study of their qualitative
and quantitative composition is extraction with a mixture
of sodium hydroxide and pyrophosphate at pH 12–13 .
The extract obtained in this case is a polydisperse system
and contains a mixture of humates and fulvates with
pyrophosphate complexes of metals and an excess amount
of an alkali and sodium pyrophosphate. Acidiﬁ cation
of the extract with hydrochloric or sulfuric acid to pH
1.5–2.0 yields a poorly soluble precipitate of humic
acids, with soluble fulvic acids remaining in solution.
The resulting preparations of humic acids contain
a considerable amount of mineral components, which
requires an additional puriﬁ cation.
An efﬁ cient way to purify colloid systems to remove
electrolytes is electrodialysis . Data on use of
membrane methods in, in particular, demineralization
of soil extracts are scarce. It seems, however, that use
of these methods to remove most part of electrolytes
that accompany humic substances will yield humic acid
preparations with increased purity.
The aim of this study was to determine the fundamental
aspects of mass transfer in electrodialysis of soil extracts
with membranes of varied chemical nature.
As object of study served alkaline extracts obtained
by treating samples of virgin chernozem, leached with
a 0.1 M solution of sodium pyrophosphate, in a 0.1 M
sodium hydroxide solution at a soil : solution mass ratio
of 1 : 5 for 24 h. The resulting suspension was centrifuged
and the alkaline extract of humic acids was separated from
the solid phase and subjected to electrodialysis with inert
or ion-exchange membranes. As inert membranes were
used an unvarnished cellulose ﬁ lm [cellophane, GOST
(State Standard) 7730–89]. In addition, the following
membranes were employed: heterogeneous MK-40 based
on a KU-2 sulfostyrene cation exchanger, MA-40 based
on an EDE-10P low-basic anion exchanger of aliphatic
nature, and MA-41 containing a AV-17 strongly basic
Demineralization of Alkaline Soil Extracts by Electrodialysis
with Inert and Ion-Exchange Membranes
V. V. Kotov, D. V. Nenakhov, K. E. Stekol’nikov, and O. V. Peregonchaya
Voronezh State Agricultural University, Federal State Educational Enterprise
for Higher Professional Education, Voronezh, Russia
Received October 23, 2008
Abstract—Mass-transfer in electrodialysis of alkaline soil extracts containing pyrophosphate ions with cellophane
and MA-40 and MA-41 ion-exchange membranes was studied. The transport numbers of hydroxide- and
phosphorus-containing ions and the degree of demineralization of the alkaline soil extracts were determined
under the conditions under study.
Fig. 1. Schematic of the installation for electrodialysis. (E)
dc power source, (ED) electrodialyzer, (1–4) electrodialyzer
sections, (Q) coulometer, (mA) milliammeter, (+) cations,
and (–) anions. Membranes: (A) anion-exchange, (C) cation-
exchange, and (Cph) cellophane.