Natural resource management

Throughout the fertilizer life cycle, there are impacts on land , air , water and nutrient cycles that need to be managed. Many of these can be minimized or even eliminated, but that requires appropriate technology and good management.

The fertilizer industry approach to environmental issues has moved from ‘end-of-pipe’ solutions, towards a pollution prevention strategy at production sites. This strategy requires an integrated, holistic view of activities. Tools have been developed to assist management, including cleaner production, life cycle assessment and industrial ecology. Each of these looks at the life cycle of the product or service to identify where the major environmental issues or problems may arise and where the most cost-effective solutions can be developed. The concept is to transform what was formerly a linear production process and, to the extent possible, make it a closed loop.

This means that mines need to be developed and operated according to the whole-of-mine-life concept, whereby previously unrecovered resources may be retrieved, former wastes converted into useful products and the rehabilitation of the site prepared from the outset.

At manufacturing sites, “closed-loop production” means recycling water within processes, capturing steam for the on-site generation of energy, using emissions from one process as a raw material for another and other techniques to increase efficiency and reduce the need for external resources.

Traditionally agriculture was a closed system. The nutrients in crops were consumed on site and returned to the soil through crop residues, manures and human wastes. Today, crops are transported from farms to urban centres, where nutrients enter the waste generated by cities. Ideally, these nutrients would be recovered and returned to the farm for re-use, but satisfactory solutions have not yet been found to do this. Given the large distances involved, such transport would generate other environmental impacts, and it is rarely economical to return the nutrients to agricultural areas, especially given the significant costs of isolating them. Very few water treatment centres anywhere implement the tertiary treatment that removes nutrients. Perhaps more difficult, urban and industrial wastes often contain heavy metals and other impurities. Because heavy metals accumulate in the food chain, applying these wastes to farmlands could raise heavy metal concentrations beyond acceptable levels. Again, there is not yet an economical technology for separating the nutrients from the contaminants.

Although agriculture itself is no longer a closed loop because of demographics, it is possible to “re-engineer” agricultural production so that it is more sustainable. Agriculture requires five types of assets: natural, social, human, physical and economic/financial capital. Best Management Practices seek to increase each of these five capital pools. Among the techniques that contribute to a shift towards “capital replenishment”, those that are most relevant with regard to fertilizer use are integrated plant nutrient management, livestock integration, conservation tillage and agroforestry.

Land

During the mining of fertilizer raw materials, the land surface and sub-surface is disturbed by activities such as the extraction of ore, the deposition of overburden, the disposal of beneficiation wastes and the subsidence of the surface. These activities could result in a wide range of potential impacts on the land, topsoil, aquifers and surface drainage systems. Additionally, the removal of vegetation may affect the hydrological cycle, wildlife habitat and biodiversity of the area.

Removal and stockpiling of topsoil for subsequent rehabilitation is carried out at many mining operations. In a number of cases, topsoil is removed and placed directly on landscaped reclaimed areas. This avoids the cost of re-transporting topsoil from stockpiles and the possible reduction of biodiversity. The re-planting of small trees from areas to be mined and the placement of dead trees on rehabilitated areas has been used to accelerate the establishment of vegetation and provide wildlife habitats.

With regard to fertilizer production sites, the major land issue relates to the soil clean-up that may be necessary when a site is decommissioned and turned over for other uses. Modern plants that apply best practices are run in such a way that this problem should be negligible when they are no longer in service, but this is not necessarily the case with older facilities. Since there are no clear guidelines on what constitutes a sufficient level of clean-up, companies may be dependent on costly and time-consuming assessments to design an appropriate clean-up.

With regard to fertilizer use, land stewardship is critical, as it is one of the major resources upon which farming depends. Fertilizer use contributes to land stewardship by helping maintain or even restore soil fertility. Plant nutrients are a critical element of any plan to reverse land degradation. By making it possible to increase agricultural productivity per unit of land, fertilizers help to protect forests and other wilderness areas that would otherwise come under the plough.

Nonetheless farmers need to manage fertilizers properly in order to moderate some potential land impacts. Some fertilizers acidify the soil. Simple corrective measures such as liming exist and are easily implemented. Fertilizers contain naturally occurring impurities that can build up in soils. The best known of these is cadmium , although other heavy metals are also present in the mineral ores used to manufacture fertilizers. Current agricultural practices are adequate to prevent this accumulation from reaching critical levels . Certain non-food plants can even be used to remove heavy metals from contaminated soil through phyto-remediation. Processes exist to remove cadmium from phosphate products, but they are economically viable only for phosphates destined directly for human or animal consumption. Furthermore, not all production processes involve the use of phosphoric acid, which is where the opportunity for cadmium removal occurs.

Air

During the mining of fertilizer raw materials, air quality can be affected by emissions of dust; exhaust particulates and exhaust gases such as carbon dioxide (CO₂), carbon monoxide (CO), nitrogen oxides (NO_x), and sulphur oxides (SO_x); volatile organic compounds (VOCs) from fuelling and workshop activities; and methane released from some geological strata.

Dust generated by vehicle traffic can be reduced through a variety of means. Where water resources are not limited, regular watering with mobile water trucks or fixed sprinkler systems is effective. Otherwise the application of surface binding agents, the selection of suitable construction materials and the sealing of heavily used access ways may be more suitable. Dust emitted during beneficiation can be controlled by means such as water sprays, baghouses and wet scrubbers. Captured dust can generally be returned to the beneficiation process.

Atmospheric pollutants emitted by the fertilizer industry can include gaseous ammonia (NH₃) and ammonium salt aerosols, nitric and nitrous oxides (NO and N₂O), fluorine – as silicon fluoride (SiF₄) and hydrogen fluoride (HF) – sulphur oxides (SO_x ), fertilizer dust and acid mists.

Naturally occurring radiation (from phosphogypsum) may also be present.

Various abatement technologies exist and are evolving constantly. For example, a recent technological breakthrough makes it possible to destroy virtually all of the N2O from nitric acid production . A few years ago, this would have been an unavoidable emission. We now see rapid uptake of this catalytic technology, fostered by financing mobilized under the Kyoto Protocol’s Clean Development Mechanism and Joint Implementation .

Water

Water quality can be affected at the mine site by the release of slurry brines and contaminants into process water. Surface waters may be contaminated by the erosion of fines from disturbed ground such as open-cut workings, overburden dumps and spoil piles and waste disposal facilities; the release or leakage of brines; and the weathering of overburden contaminants, which may then leach.

Large volumes of water are typically required by mining and beneficiation activities. Furthermore, water is often pumped from the excavations or from nearby wells to maintain a dry, safe and efficient operating environment for the miners and their equipment. This may lead to a fall in the level of the local water table, affecting the surrounding ecosystem and potentially resulting in competition with other users.

In some locations, measures have been taken to confine the area affected by water table depression and protect the surrounding ecosystem. Waste water produced during the extraction stage can be used for downstream processing operations, reducing the demand on other sources. Where appropriate, water of suitable quality has been used for the irrigation of local farming operations.

Elevated sediment levels in surface water are caused largely by uncontrolled water run-off, mobilizing the fines from disturbed areas. Mining operations have employed a variety of control techniques, including:

• Lining drainage channels with large rocks to prevent erosion and trap sediments;
• Landscaping overburden to create a flatter, more stable land area slowing the rate of run-off;
• Rehabilitating disturbed areas as soon as is operationally possible, through seeding with grass, spreading of mulch, laying of geofabric or crossripping with bulldozers.

In some situations, natural drainage systems have been channeled around mining areas or vegetation buffer zones have been retained to reduce the movement of sediments off-site. These measures have been strengthened by the use of silt traps and settling dams to retain and clarify contaminated water before release.

Tailing brines may potentially contaminate surface or ground waters. Operations commonly employ monitoring and containment systems to detect and control spillages and prevent widespread contamination from occurring.

Water and steam are inputs in the manufacture of several fertilizer products, where others produce them. Emissions into water vary from one production process to another; but, in general, best practice technologies and good management make it possible to minimize these emissions to acceptable levels. IFA provides environmental benchmarking to help its members chart a course towards ever cleaner production, and companies share their experiences through the activities of the Technical Committee , which helps to drive continual improvement across the industry.

Improper fertilizer management in farmers’ fields can lead to excess nutrients leaching into groundwater or contributing to eutrophication of surface water .

Nutrient cycles

Agricultural systems are ecosystems that are managed to increase the production of food, feed, fibre and energy. One important limit on the productivity of natural ecosystems is the availability of nutrients in plant-available forms. On a local level, a number of nutrients may be lacking, but nitrogen and phosphorus are generally the limiting factors in natural ecosystems because plants require them in greater quantities than other elements.

Fertilizer production and use intervenes in nutrient cycles in two principal ways: moving nutrients from where they are abundant to where they are needed by farmers and transforming the nutrients into plant-available forms.

Each nutrient cycle has its own particularities. Phosphorus tends to be relatively immobile, even in plant-available forms. The phosphorus adsorbs to soil particles and remains in the soil unless physically transported through erosion. Nitrogen is much more mobile. Inert dinitrogen is all around us in the air we breathe, but this form cannot be used by plants. A number of natural processes transform this dinitrogen into plant-available forms, but these natural processes are not sufficient to support today’s growing population. The fertilizer industry therefore fixes nitrogen through the industrial synthesis of ammonia, which is then used directly by farmers or incorporated into other fertilizer products. Once converted from its inert to its reactive form, nitrogen tends to persist in the environment and cycle through several forms before eventually being reconverted to dinitrogen. The fertilizer industry works closely with the scientific community to improve nitrogen management in order to minimize unwanted environmental impacts while safeguarding adequate food production.