In the late 20th century, 60% of nickel production was based on the matte smelting of sulfide ores, which did not lend itself to production of ferronickel. According to 2003 data, the share of laterites in primary nickel production was reported to be 42%. World annual production of ferronickel in 2014 was around 250,000 tonnes. The two largest producers were BHP Billiton and Société Le Nickel. Laterite ores are often used to supply the production process. The RKEF process is often used. The energy consumption per tonne of product is high for laterite ores because of the low-grade feed, and hence produces a lot of waste slag and gaseous pollution. Generally, over 90% of the furnace output is in the form of slag. The technique of refining molten ferronickel is a topic for specialists, and because of ore content variability the processes might even need to be tailored by source: for example the Larco process of Greek ores. "The main reason for adding nickel in ferrous alloys is to promote an austenitic microstructure. Nickel generally increases ductility, toughness and corrosion resistance." Nickel pig iron is distinguished from ferronickel by the former's low weight fraction (4-10%) of nickel and high carbon content (>3%). In contrast, ferronickel is a relatively pure binary alloy.