Sulfuric acid has many uses. World production in 2001 was 165 million tons, worth about $8 billion US dollars. Uses include ore processing, fertilizer manufacturing, oil refining, wastewater processing, lead acid batteries, and combining chemicals for scientific reasons. For example, phosphate rocks are reacted with sulfuric acid to produce soluble phosphates, useful in fertilizers. This reaction is also used to make phosphoric acid, useful in soda. Potassium compounds are dissolved in sulfuric acid to produce potassium sulfate, useful in fertilizers. Ammonia is also reacted with sulfuric acid to produce ammonium sulfate. These three chemicals are solids and provide the three main minerals needed in plants. Lead acid batteries use sulfuric acid as their electrolyte.