Physicochemical Aspects of Phosphorite Powder
Decomposition by Weak Acid
N. V. Shul’ga and N. P. Krut’ko
Institute of General and Inorganic Chemistry, National Academy of Sciences of Belarus, Minsk, Belarus
Received December 3, 2010
Abstract—Fundamental aspects of phosphorite powder decomposition by citric acid were studied.
INORGANIC SYNTHESIS AND INDUSTRIAL
ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 8, pp. 1329–1334. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © N.V. Shul’ga, N.P. Krut’ko, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 8, pp. 1264–1269.
The problem of supply of phosphate raw materials
to industrial plants requires that low-grade phos-
phorites should be used for manufacture of fertilizers,
with a technology for their process developed . As
an alternative to the conventional and expensive water-
soluble phosphorus fertilizers with an efficiency of 25–
30% is also considered use of phosphorite powder (PP)
after its chemical or mechanochemical activation .
It is commonly recommended to evaluate the
suitability (activity) of phosphorite powder as a
fertilizer by the procedure described in . A
phosphorite powder is considered active if no less than
60% of P
it contains is extracted into a 2% aqueous
solution of citric acid .
Using the procedure  when working with
phosphorite powder, we encountered certain diffi-
culties which give no way of making unambiguous
conclusions about the activity of both the starting PP
and its separate fractions.
The goal of our study was to examine physico-
chemical aspects of the decomposition of phosphorite
powder in weakly acid media and develop criteria for
evaluation and comparison of the activities of PP
samples of various chemical compositions.
As object of study served PP from the Polpino
deposit (Bryansk oblast), with a comparatively low
content of phosphorus (13.3 wt % P
procedure used for its analysis and the results obtained
were reported in . The starting phosphorite powder
was separated by sieving into fractions that contain,
depending on dispersity, phosphorus in an amount ωP =
1.26 to 7.46 wt %, which constitutes 2.9–17.1 wt % in
terms of P
The chemical composition of the phosphate
component for the –0.1 mm fraction (80% in PP)
corresponded to a bulk formula Ca
We recovered phosphorus with aqueous solutions
of citric acid (CA), with a concentration c = 0.1–
2.0 wt %, which made it possible to vary the initial
in the suspension within the respective range
2.80–2.06. The volume of the CA solution in the main
series of experiments was 100 ml, with 200 ml taken in
some cases. The l : s ratio (ml g
) was varied within
the range 12.5–100 at c = 2% and within the range
100–2000 at CA concentrations of 2 to 0.1%.
When evaluating the degree α (%) of phosphorus
extraction from the phosphorite powder, we transferred
a weighed portion of the substance into a citric acid
solution and the mixture was agitated with a magnetic
rabble at room temperature for a certain time τ, after
which the suspension was rapidly filtered on a Buchner
funnel (“blue band”) by the procedure described in .
In some cases, the suspension was maintained at a
higher temperature in PP decomposition.
The pH value of the suspension and filtrate was
monitored with EV-74 pH-meter .
There exists opinion that phosphorite powder
decomposes in a soil solution via the stage in which
, whose further conversion to