Agriculture Reference
In-Depth Information
pyrophyllite, mica, smectite, vermiculite, chlorite, attapulgite, sepiolite). Only a
small number of clay minerals are components of industrial clays: kaolinite (kao-
lin), montmorillonite (bentonite), talc (talc), vermiculite (vermiculite), and chrys-
otile (asbestos).
These materials are being used more and more because of their abundance, their
ease to handle, and their potential in various applications, including fertilizers. The
interest in clay minerals is also because of some of their special behaviors such as
swelling, adsorption, rheological and colloidal properties, and plasticity (Santos
1989
; Konta
1995
).
There are some examples of clay minerals used in conjunction with fertilizers.
Bentonite avoids a major problem in the manufacture of fluid fertilizers, that is, the
difficulty to obtain formulations with a high concentration of nutrients. Particularly,
dispersed bentonite increases the viscosity of formulations with more than 12 % of
K
2
O, preventing the precipitation of crystals (Kornd¨rfer and Datnoff
1995
).
Another example is a fertilizer produced in Canada, in which molten elemental
sulfur is incorporated into bentonite, thereby obtaining a granulated fertilizer that
facilitates the application of the product (Boswell et al.
1988
; Saik
1995
). There are
still reports with rocks containing biotite or phlogopite, which show potential as
nutrient source (Nascimento and Loureiro
2004
). Thus, exploration of mineral
diversity is important to discover new fertilizer sources and to design new methods
of implementation and their availability.
However, the cation-exchange behavior in clays is quite different from that
observed in zeolites. Since the structure behaves as a set of stacked nanometric
lamellas, the ionic accessibility depends on its appropriate exfoliation. This phe-
nomenon occurs spontaneously in aqueous suspensions, but in dry material, there is
a tendency to re-agglomeration (Santos
1989
; Konta
1995
). Thus, applications of
clay minerals where their high surface must be accessible are only possible after
surface modification of clays, which exposes the clay nanostructure. This area has
received much attention because it allows expanding the possibilities of using clays,
creating new materials and new applications, mainly in nanocomposites
production.
Studies have demonstrated that structure of clay minerals can be modified by
pillarization (Luna and Schuchardt
1999
; Pergher and Sprung
2005
) or exfoliation
phenomena (Murray
2000
). Exfoliation takes places by a primary ion exchange (Na
+
or Ca
2+
) by larger ions, resulting in a interlayer expansion. This process was
demonstrated using NH
4
+
, from the urea hydrolysis, which makes the process
interesting for agriculture (Gardolinski et al.
2001
). However, the most significant
recent studies involve surface modification of clays with polymers or
compatibilizers, allowing exfoliation of the clay within the polymer matrix.
A recent study conducted by Kim et al. (
2011
) proposed the intercalation of a
large amount of complexed urea and magnesium in montmorillonite. The efficiency
of the product was measured and confirmed by considerable suppression of the
emission of both NH
3
and N
2
O. It was also noted that these effects improved the
nitrogen uptake by crops and, therefore, the productivity. Figure
11.3
illustrates the
behaviors of intercalated urea molecules in soil. However, the authors studied the
