Environmental risk of waste and its management - Environmental Deterioration and Contamination: Problems and their Management - page 155

use of phosphogypsum is in agricultural applications. Phosphogypsum has been used
in agriculture as a source of calcium and sulfur for soils that are deficient in these
elements. When phosphogypsum is used as a fertilizer, it is simply spread on the soil.
When used for pH adjustment or sediment control, it is tilled into the soil. Phosph-
ogypsum's only limitation for agricultural use is its radioactivity: it must not exceed
10 pCi/g.
An estimated 221,000 metric tonnes of phosphogypsum are taken from the phos-
phogypsum stacks and used in agriculture every year in the US. There is no limitation
on the amount of material that can be applied, and farmers do not have to maintain
certificates or application records (EPA Fertilizer, 2013). Environmental bodies in the
US encourage developers to find new ways to utilize sulfur waste for amending soil.
Ilyas et al. (1997) and Ahmed and Ugai (2011) investigated the chemical changes in
soil and durability of gypsum effect in detail and their results do not contraindicate
the long-term use of phosphogypsum on agricultural soil.
Degirmenci et al. (2007) applied phosphogypsum in soil stabilization, and Nayak
et al. (2011) proved its beneficial effect on soil physico-chemical properties, microbial
load and enzyme activities, up to 10% amendment. Hao et al. (2005) measured the
effect of phosphogypsum on greenhouse gas emissions during cattle manure compost-
ing and found a significant decrease. Adams et al. (2007) used phosphogypsum for the
immobilization of mercury in soils in Venezuela.
Flue gas desulphurization (FGD) gypsum is produced by removal of waste gases
from the smokestacks from burning of coal and other materials. Approximately 20
million tonnes of FGD residues are produced annually in the USA alone (Nature's
Way, 2013). These materials have high gypsum content, but they may also contain
impurities such as boron (B), aluminum (Al) and other metals. Depending on the
source, they may contain significant amounts of radioactive radon (Ra). This type of
waste should be thoroughly analyzed before being used on soil.
Plasterboard waste and gypsum casting molds are available for reuse in soil after
some preparation. Soil application of plasterboard waste has been demonstrated to be
nearly identical to application of agricultural gypsum (Yost, 1998; MOKKA, 2014).
Options include grinding the gypsum into powder, or chipping it to form mulch. Its
paper content is potentially beneficial as a carbon source and to retain moisture.
Gypsum contains both calcium and sulfur which are essential nutrients for plants.
Additionally, it has been claimed that recycled plasterboard often works better than
agricultural gypsum due to a wider profile of trace elements that are beneficial to plant
life (Nature's Way Resources, 2013).
Other means of sulfur waste utilization such as composting together with biomass
are recommended conditionally, due to the possible H 2 S production under anoxic or
anaerobic conditions. Disposal with municipal waste is prohibited due to the formation
of H 2 S in the course of anaerobic digestion, thus impairing the quality of the produced
biogas.
There are several other chemical substances and valuable materials in wastes and
by-products which are suitable for supplementing depleted constituents in agricul-
tural soils or in cover materials of landfills and other disposal facilities. In addition
to supplementing missing soil components, carbon can be trapped in the soil solid
matrix over the long term, instead of emitting CO 2 into the atmosphere. This
kind of carbon sequestration may reduce greenhouse gas emissions and improve