Comparative effect of chrysotile leaching in nitric, sulfuric and oxalic acids at room temperature

• Chrysotile was leached at pH 1 in nitric, sulphuric and oxalic acid at room temperature.
• 30 days nitric leaching produces an intense dissolution.
• 30 days of sulphuric leaching lead to an amorphous siliceous material.
• 30 days of oxalic acid also produces an amorphous material and precipitation of glushinskite.

The acid leaching of chrysotile was investigated in different acid media with the aim of quantifying and obtaining insights into the dissolution mechanism. Chrysotile was leached in batch reactors for 1 to 30 days at 25 °C and pH 1 in aqueous solutions of nitric and sulfuric acid and different concentrations of oxalic acid (50, 100 and 200 mmol L− 1). The combined analysis of solutions and solids by XRD and FTIR shows different effects: nitric acid induces a strong dissolution after 30 days, lowering the crystallinity of the sample and initiating the transformation of the chrysotile into an amorphous siliceous material. In the case of sulfuric acid, the dissolution is so intense that it is able to destroy the brucitic sheet of chrysotile, leading to an amorphous silica byproduct. Finally oxalic acid is also able to induce amorphization of chrysotile and the precipitation of glushinskite (MgC2O4·2H2O). As the concentration of oxalic increases from 50 to 200 mmol L− 1 the amorphization process becomes faster. Finally, the relative effectiveness of acid attack to chrysotile is oxalic acid (9 days) > sulfuric acid (30 days) > nitric acid.