THE PHOSPHATE LIFE-CYCLE: RETHINKING THE OPTIONS FOR A FINITE RESOURCE

摘要

Of the four major plant nutrients (nitrogen (N), phosphorus (P), potassium (K) and sulphur (S)) required to grow crops for food, feed, fibre and bio-energy, the global resource of P is least. Of the phosphate rock (PR) that is mined each year more than 85% is processed for use in agriculture, as fertiliser to grow crops and as an additive to animal feed. Unlike some recent papers, which have analysed the threat of depletion by, calculating the rate of exhaustion of current reserves, (Smil, 2000; Steen, 1998; Gunter, 2005; Smit etal, 2009) this paper explores the opportunity offered by conservation, arguing this opportunity should be seized now, irrespective of the quantity and status of unmined reserves. Conservation is an achievable, measurable objective which will deliver benefit to all stakeholders. So what are the practical options for managing this finite resource? To conserve the world's limited P resource it must, first, be mined, processed and used more efficiently, with a particular emphasis on efficiency of use in agriculture. The conservation effort does not however, stop there. Phosphorus removed from the land must be recovered and reused/ recycled effectively. In parallel, value streams that come from the process of mining PR and making phosphoric acid can also be exploited, most notably the recovery of uranium from the phosphoric acid for use as a fuel for nuclear energy (Hilton et al, 2009a) and the use of the co-product phosphogypsum in agriculture (Hilton, 2006). Accordingly, this paper seeks first a sustainable management approach, derived from linking innovative micro-level 'closed system' concepts about the behaviour of soil and fertiliser P with the macro-level perspective of the efficient use, and reuse, of the global phosphate resource for food and energy security; secondly, it examines risks and benefits in the proposed managed P life-cycle with a view to setting out an achievable, socially acceptable and environmentally sustainable management regime for a resource that might otherwise deplete unnecessarily quickly or even run out. Calculating phosphate reserves and relative depletion rates may be, by contrast, a very elusive issue given a) the extreme commercial sensitivity of the data, and b) the dependency of many developing economies on access to phosphate fertiliser for their agriculture, on the industry's contribution to their national GDP, and on hard currency earnings from sales of rock and phosphate products in the global market.