Historical and technical developments of potassium resources

Highlights

• The development of the potash industry from 1700 to the present days is reviewed.

• A historical analysis reveals the origin of the current limitations of the potash market.

• Past experiences provide guidelines for the successful development of a new generation of potash fertilizers.

Abstract

The mining of soluble potassium salts (potash) is essential for manufacturing fertilizers required to ensure continuous production of crops and hence global food security. As of 2014, potash is mined predominantly in the northern hemisphere, where large deposits occur. Production tonnage and prices do not take into account the needs of the farmers of the poorest countries. Consequently, soils of some regions of the southern hemisphere are currently being depleted of potassium due to the expansion and intensification of agriculture coupled with the lack of affordable potash. Moving away from mined salts towards locally available resources of potassium, such as K-bearing silicates, could be one option to improve this situation. Overall, the global potash production system and its sustainability warrant discussion. In this contribution we examine the history of potash production and discuss the different sources and technologies used throughout the centuries. In particular, we highlight the political and economic conditions that favored the development of one specific technology over another. We identified a pattern of needs driving innovation. We show that as needs evolved throughout history, alternatives to soluble salts have been used to obtain K-fertilizers. Those alternatives may meet the incoming needs of our century, providing the regulatory and advisory practices that prevailed in the 20th century are revised.

Introduction

Fertilizers are an essential component of crop production (Scherer et al., 2002) particularly to replace nutrients removed from the soil during harvesting (referred to as ‘offtake’; Sheldrick et al., 2002). The main elements provided by fertilizers are nitrogen (N), phosphorus (P) and potassium (K) (Lüttge and Clarkson, 1989, Scherer et al., 2002). N and P are the essential building blocks of nucleic acids and adenosine triphosphate (ATP), the biological energy carrier (Frink et al., 1999, Smil, 2004). K is necessary to regulate the electrochemical (and osmotic) potential across the cell membrane (Darst, 1991, Lüttge and Clarkson, 1989, Öborn et al., 2005, Römheld and Kirkby, 2010). N-fertilizers are manufactured from ammonia which is synthesized with the Haber–Bosch process using N₂ from the air and H₂ from fossil fuels as reactants (Hager, 2008, Smil, 2004, Russel and Williams, 1977). P- and K-fertilizers are products of the mining industry (Manning, 2010, Russel and Williams, 1977). P-fertilizers are obtained from phosphate rocks containing the mineral apatite (MacDonald et al., 2011, Manning, 2010, Manning, 2012, Obersteiner et al., 2013, Scholz and Wellmer, 2013). K-fertilizers are presently obtained from sedimentary rocks (Supplementary Material) that are mixtures of soluble salts (most importantly KCl) referred to as potash when traded as a commodity. Although the K⁺ ion is the form of potassium released by commercial fertilizers, the total K content in different potash products is conventionally expressed as equivalent weight percent of potassium oxide (wt % K₂O).

Our anthropocene era (Crutzen, 2002) sees a complex interplay of human activities that outcompetes nature in both time and space, thus resulting in a force of geological relevance (Crutzen, 2002, Crutzen, 2006). Since the industrial revolution, mining significantly contributes to anthropogenic geological change (Azapagic, 2004, Crutzen, 2002). The pressing challenge for human development is to formulate a model for progress which meets the needs of the present without compromising the ability of future generations to meet their own needs (Brundtland, 1987). The underlying concept is sustainability, a multidimensional construct that according to a classic approach comprises three main domains: i) society, ii) economy, and iii) environment (Azapagic, 2004, Brown et al., 1987, Cordell et al., 2009, Costanza and Patten, 1995, Dold, 2008, Lélé, 1991, Leonardos et al., 2000, Mueller et al., 2012, Tilman et al., 2002). In this framework the shortcomings of current industrial paradigms, fertilizers included, are noteworthy.

Societies currently need fertilizers to improve agricultural yields and ensure food security. Concerns have been raised on the scarcity of non-renewable P reserves (Cordell et al., 2009). Although such concerns have been proved to be unjustified (Scholtz and Wellmer, 2013) and part of a historically recurring debate (Ulrich and Frossard, 2014), the problem of the accessibility of fertilizers from the poorest societies remains less discussed. Phosphate rocks are mined in more than thirty countries dominated by China, USA and Morocco (Cordell et al., 2009, Manning, 2012, Obersteiner et al., 2013). In the case of potash, scarcity of reserves has not been reported so far. Ores are expected to last about 400 years at the current rate of extraction, based on estimates published by the United States Geological Survey (Jasinski, 2011). However, potash production is strongly dominated by three countries: Canada, Russia and Belarus produce more than 90% of world potash (Anderson, 1985, The New York Times Editorial Board, 2013, Manning, 2010, Manning, 2012, Rittenhouse, 1979). Thus, in the Global South large amounts of potash have to be imported from the northern hemisphere. An emblematic example is given by Brazil that in 2011 imported 4,357,186 t of K₂O, more than 90% of its current potash need (FAOSTAT database, 2013). Approaches towards national self-sufficiency may be sought for, especially for developing countries, to allow stronger negotiation position on both the international stage and the agricultural world markets.

Economy is the primary driver of industries, fertilizers included. Overall, global potash revenues accounted for US$26 billion in 2012 (Manning, 2012). A common impression is that the limited geographical distribution of productive potash mines can result in trades that favor producers rather than buyers (The New York Times Editorial Board, 2013). As an example, the potash market experienced a certain degree of monopolization and price cartelization at its inception, thus shaping its current status (Anderson, 1985, Hayes, 1942, Kreps, 1931, Kurrelmeyer, 1951, Tosdal, 1913). The free-on-board price for 1 t of potash peaked at US$800 in 2008. Since then, price has been falling due to major market readjustments, but remains high for many farmers (about US$300/t F.O.B. as of 2014), in part reflecting the initial capital cost of the few deep mines in exploitation. Most importantly, inefficient logistics and infrastructure increase the final cost for the farmers in the poorest countries. In particular, fertilizer use statistics for Africa demonstrate that despite supporting 15% of the world's population, this continent only uses 1.5% of the world's K-fertilizers (Manning, 2012), an unsustainable situation in the perspective of its continuous population growth. Exploration for and opening of conventional deep mines are lengthy and costly processes that seem impractical for the Global South. Thus, new paradigms for the current potash market could be proposed to meet the needs of those who cannot access fertilizers on the grounds of cost or availability.

Environment is the third imperative that a sustainable model needs to confront. Current mining activities raise questions on deterioration of air and water quality as well as landscape modification/degradation (Azapagic, 2004, Dold, 2008, Anonymous, 2001, Russel and Williams, 1977). From a soil perspective the imbalance in offtake through cropping impoverishes the quality of the soil. However, different situations are observed for the three main nutrients. N is approximately in balance in the world soils meaning that agronomic inputs (fertilizers plus manure) equal the outputs (crop harvests; Sheldrick et al., 2002). Similarly, P global inputs exceeded the outputs in the year 2000, although 30% of the global cropland still experienced a deficit (MacDonald et al., 2011). Balanced levels of N and P in soils that are subject to through drainage suggest excessive application of fertilizers that leads to the critical problem of eutrophication of the aquatic ecosystems (Cordell et al., 2009, Frink et al., 1999). For K, in contrast, deficits have been reported especially for the African continent (Sheldrick and Lingard, 2004) as well as for China and India (Römheld and Kirkby, 2010). A significant reduction in K use has been observed also in many European countries (Öborn et al., 2005, Somerwill et al., 2012). Low K levels suggest agronomic practices overly intense with respect to the amount of potash replenished by fertilizers. If potassium deficits are not corrected, fertility loss will have to be faced. While such correction can be relatively easily implemented in the northern hemisphere, the deep leached soils of the Global South might be at risk. Furthermore, even if actual potash fertilizers from the North should reach the South, a high carbon cost for transportation, along with the effects of salinization and chloride, or loss through drainage, will have to be handled (Bernstein, 1975, Cordell et al., 2009, Lodge, 1938, Rozema and Flowers, 2008). Alternative approaches have been put forward. For example, the concept of agrogeology proposed as early as 1862 and redefined by van Straaten, aims at fertilizing the soils of the Global South by using slow nutrient-releasers of geological origin such as unprocessed P- or K- bearing rocks (petrofertilizers) (De'sigmond, 1935, Leonardos et al., 1987, Leonardos et al., 2000, Van Straaten, 2002, Van Straaten, 2006). Movements such as Rochagem have promoted this concept (remineralize.org, 2014).

Overall, concerns on the possibility of a sustainable agriculture for the 21st century seem justified and the role of fertilizers appears pivotal. In this paper we focus on K-fertilizers. The sustainability challenge is to develop a potash market that takes into account affordability, local availability and compatibility with crops and soil composition (Van Straaten, 2006). To achieve this market, it is essential to understand the historical and social context (Cordell et al., 2009, Scholz and Wellmer, 2013, Ulrich and Frossard, 2014) that has led to the present-day situation. Therefore, this paper addresses the history of potash production from 1700 to the present on the basis of several multidisciplinary sources. The intimate interconnections between geopolitical, economic and technological factors that have led to the current potash sector are highlighted. Food security and the possibility of reducing the gap between need and access to potash may very well depend on a holistic interpretation of such interconnections.