1070-4272/05/7811-1761C2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 11, 2005, pp. 1761!1766. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 11,
2005, pp. 1796!1800.
Original Russian Text Copyright + 2005 by Lokshin, Ivlev, Tareeva.
AND INDUSTRIAL INORGANIC CHEMISTRY
Leaching-out of Lanthanides from Waste Phosphosemihydrate
with Sulfuric Acid Solutions of Increased Concentration
E. P. Lokshin, K. G. Ivlev, and O. A. Tareeva
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials,
Kola Scientific Center, Russian Academy of Sciences, Apatity, Murmansk oblast, Russia
Received January 26, 2005
Abstract-Leaching-out of lanthanides from waste phosphosemihydrate with 20330% sulfuric acid solutions
Upon processing of the Khibiny apatite concentrate
by the semihydrate technology to obtain wet-process
phosphoric acid, the main part of lanthanides is con-
tained in calcium sulfate semihydrate [technical name
of the product: phosphosemihydrate (PSH)] [1, 2].
Sulfuric acid leaching can be used for recovery of
lanthanides [3, 4].
In [3, 4], the sulfuric acid leaching was performed
with low-concentration solutions (c
< 10 wt %)
at high l : s = (5310) : 1. A high degree of recovery
of lanthanides into solution was achieved (up to 84%),
but the concentration of lanthanides in solution,
, did not exceed 1 g l
. All attempts to raise
in leaching solutions failed.
In the process, it was established that, in leaching
of several portions of PSH with the same sulfuric acid
solution at l : s = 3 : 1, leaching time of 233 h, and
subsequently raised to 12324 wt %, the con-
centration of lanthanides in solution increased to
and more, but the recovery of lanthanides in
each stage did not exceed 30340% and decreased as
became higher . With a solution with
= 25 wt % and l : s = 5 : 1, the recovery of
lanthanides into solution was 30% at c
0.34 g l
The experimentally determined concentration of
lanthanides in leaching solutions is considerably lower
than the solubility of lanthanide sulfates in sulfuric
acid solutions. However, the reason for this fact has
not been established.
The large volumes of the solutions involved and
low concentration of lanthanides in them strongly
hinder their processing to recover lanthanides and
subsequent utilization in manufacture of wet-process
phosphoric acid. This makes studies aimed to improve
the leaching technology a matter of current interest.
The goal of this study was to examine leaching-out
of lanthanides from waste PSH with sulfuric acid
solutions of medium concentrations (20332 wt %) and
to reveal the factors limiting the accumulation of lan-
thanides in leaching solutions.
Experiments were carried out with waste PSH
with a moisture content of 20 wt %. It contained
0.56 wt %
in terms of a dry product.
The influence exerted by the conditions of leaching
with sulfuric acid solutions of medium concentration
=20332 wt %) on the processing efficiency
was analyzed. The leaching time was 1 h, because this
time is sufficient according to . After the leaching
was complete, the solid phase was separated from the
solution by filtration. In some of the experiments,
the same portion of the sulfuric acid solution was used
to successively process two portions of the starting
PHS (double-stage leaching). The concentration of
the sum of lanthanides c
mined by the oxalate gravimetric technique, in which
the relative determination error was 0.3 rel % and
more for the lanthanide concentrations in the range
under study . The concentrations of individual
oxides were determined by atomic-emission spectrom-
etry with inductively coupled plasma on a Perkin3
Elmer Plasma 400 instrument. The sums of lan-
thanides determined by different methods were in
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