The vermiculite from Paulistânia, State of Piauí, was used to study a release of magnesium by acid dissolution. The material was ground and sieved to separate two fractions: 0.50 to 0.15mm and < 0.10mm. Each fraction was divided into three parts, two of which were heated respectively to 550°C and 950°C in a muffle furnace for one hour. These vermiculites were treated with concentrated sulfuric acid and concentrated phosphoric acid in order to evaluate their efficiency in acid dissolution of vermiculite. A release of magnesium in relation to a quantity of sulfuric acid added and a amount of calcium carbonate necessary to neutralize a residual acidity of the product were also investigated. The sulfuric acid was just as effective as phosphoric acid in the dissolution of vermiculites and the release of magnesium. The particle-size and heat treatment of vermiculite had no influence on the amount of magnesium released by acid dissolution. The addiction of sulfuric acid to vermiculite in equal amount released more than 80% of magnesium. A quantity of calcium carbonate necessary to neutralize the residual acidity of the product was about one half the weight of the vermiculite.
vermiculite; magnesium; acid dissolution