1070-4272/05/7809-1383C2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 9, 2005, pp. 1383!1385. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 9,
2005, pp. 1409!1411.
Original Russian Text Copyright + 2005 by Karapetyan, Senichenkov, Zenin, Ryabova.
AND INDUSTRIAL INORGANIC CHEMISTRY
Kinetics of Dissolution of Glassy Fertilizers
K. G. Karapetyan, V. A. Senichenkov, G. S. Zenin, and M. N. Ryabova
St. Petersburg State Polytechnic University, St. Petersburg, Russia
Northwest State Correspondence Technical University, St. Petersburg, Russia
Received March, 3, 2005
Abstract-Slowly soluble phosphate glasses are a promising material for new environmentally safe fertilizers.
The kinetics of the dissolution of phosphate glasses used for the development of fertilizers was studied.
Modern nature management is impossible without
application of mineral elements, because ions of
potassium, magnesium, calcium, phosphorus, boron,
and trace elements are irrevocably withdrawn from
soil together with agricultural products. Existing min-
eral fertilizers have a number of principal drawbacks
connected with their crystal structure and constant
composition. These fertilizers are easily washed away
and weathered from the soil, which gives rise to
extreme workloads on soil microorganisms and root
systems of plants. Annual world production and ap-
plication of fertilizers reaching 400 million tons is not
only prodigal, but also environmentally dangerous, as
no less than 50% of fertilizers goes to subsoil waters
and is weathered, causing environmental pollution.
The cardinal way of overcoming these drawbacks
is to abandon traditional crystalline fertilizers and to
develop essentially new highly effective fertilizers
based on glassy amorphous materials. Glass is one of
the most promising among these materials because
of its favorable physical and chemical properties and
feasibility of processing.
In the early 1980s, phosphate glasses were used to
develop a new generation of fertilizers . These fer-
tilizers of the prolonged action are based on glassy
potassium, magnesium, and calcium metaphosphates
doped with microelements. Their preparation was
based on long-term experience in the field of develop-
ment of optical glasses and ion-exchange processes.
As a result of these studies [1, 2], a new type of
glassy fertilizers (AVA) was developed; their high ef-
ficiency and environmental cleanliness are due to the
high-temperature synthesis of phosphate systems,
quenching of the structural state of the components
in the form assimilable by plants, and their variable
composition providing easy adaptation to regions of
use, to types of soils, and to the kind of crops.
The rate of dissolution of such glasses depends on
their chemical composition. Glass components, K, Ca,
and P oxides, are nontoxic. Such glasses provide
egress of the required compounds from the glass into
the environment. The dissolution of a glass in water is
accompanied by a chemical reaction between the glass
and water, which results in cleavage of the >P3O3P<
bonds and passing of phosphate ions into solution.
Metal ions contained in the glass together with P
pass simultaneously into the solution at a rate deter-
mined by the rate of the glass dissolution. The soluble
phosphate glass can be used for delivering fertilizers
with a specified intensity and substances for protec-
tion of plants.
According to published data [3, 4], the dissolution
of phosphate glasses involves several steps: selective
passing into a solution (leaching) of cations within
the framework of internal diffusion and hydrolytic de-
gradation of the anionic skeleton. However, the most
important is the thermodynamically nonequilibrium
structure of glasses, so that all the components remain
in the cytosoluble state and are accessible to plants,
and the glass dissolution is slow, with a constant
thickness of the destroyed granule layer.
Various macro- and microelements are necessary
for successful vital activity of plants. They are intro-
duced in a balanced proportion and are not subject to
Owing to specific physicochemical properties,
the rate of dissolution of a glassy fertilizer granule
strongly depends on temperature. For example, at
50oC they are dissolved within 3 months and at 20oC,
within 27 months (Fig. 1).
After introducing the fertilizers into a soil, they
slowly (within several years) dissolve to release con-
secutively chemical components feeding plants.