Hydrothermal synthesis of zeolites from a volcanic ash by alkaline treatment and their potential application in the removal of NH₄⁺, Pb²⁺, Zn²⁺ and Mn²⁺

This paper reports the results of an investigation carried out to examine the possibility of obtaining zeolitic material with high adsorption capacity from a Peruvian volcanic ash. The direct application of the zeolitic product is in the treatment of effluents from industrial plants and mining operations. The experiments were carried out in an autoclave reactor using solutions with different concentrations of NaOH, varying temperature (over the range 25-200°C) and the contact time between the volcanic material and the solution over the range 4-24 hours. The product obtained was characterized by means of diffractrometric and scanning microscopic analysis (SEM) as well as specific surface area and cation exchange capacity (C.E.C.) determinations. The results showed that different types of synthetic zeolites are produced as a function on the temperature, NaP₁ zeolite at temperatures of 80-100°C and analcime and hydroxycancrinite at higher temperatures. The highest C.E.C., around 410 meq/100g, corresponds to the product obtained at 100 °C with high formation of NaP₁ zeolite. Whit the zeolitic product obtained after attack with a 2,5 M NaOH solution, varying temperature and solution/volcanic material contact time, were further characterized by cation exchange tests using solutions containing NH⁴⁺, Pb²⁺, Zn²⁺ and Mn²⁺ .(author)