METHOD OF SYNTHESIS, FUNCTIONALIZATION AND ZEOLITE APPLICATION IN THE ADSORPTION PROCESS OF ARSENIC DISSOLVED IN WATER.

摘要

The present invention relates to a method for obtaining crystalline nano porous aluminosilicates, which are distinguishable from conventional zeolites by the fact that the chemical nature of the surface thereof has been designed so as to allow the adsorption of anionic species such as as As (III) and As (V) to be adsorbed which are found in groundwater in Mexico and worldwide For its particular characteristics, zeolites have been extensively studied as catalysts, cation exchangers and adsorbents for neutral molecules. The present invention further relates to the modification of the chemical nature of the zeolite surface, so that it allows anionic species instead of cationic species , commonly adsorbed by a zeolite, to be adsorbed. There is also described a process for the obtention of W- and P-type zeolites which surface has been chemically modified so that the advantages provided by its structural features may be exploited, and the adsorption of both neutral and anionic species suc h as As(III) and As(V), made possible. The W and P zeolites are prepared from an industrial by-product of no commercial value such as the Mexican fly ash and the use thereof may be extended as another silicon source (geothermal silica), a clay (kaolin) or a natural zeolite (clinoptilolite for example). The Zeolites modified with monovalent salts (NH4 l), divalent salts (Fe (ll)) and trivalent salts (AI (III)), were characterized in detail. This characterization was complemented with a balance, kinetics and thermodynamics survey relative to the adsorption process of As (III) and As (V) on the resulting modified zeolites. The present invention further relates to the establishment of an accelerated aging process by rapid saturation of the adsorbent surface with As (V) and As (III) and, also, relates to the definition of a process for increasing the useful life the adsorbent by the regeneration thereof. As a result of the present invention, there are two technically viable methods . The f irst method being that for the synthesis of zeolite W, which involves direct recrystallization of the fly ash (KOH / ash 0.33, 175 ° C, 16 h) and the second method being that for obtaining zeolite P (NaOH / ash 1.04, alkaline fusion: 600 ° C, 2 h, crystallization, 120 ° C, 16 h) which involves the recovery-recrystallization of the fly ash. There is still a further method described for the modification with aluminum salts (III), having the same chemical nature as that of the surface of both zeolites to confer an estimated capability for adsorbing As (V) anionic species of up to 57 mg / g WMOD zeolite, and 60 mg / g of PMOD zeolite. The modification of the P zeolite with a Fe (ll) salt provides the WFE zeolite with an estimated capacity of 1.43 mg of As (lll) / g of WFE. zeolite. The Accelerated aging with the use of an As(V) solution resulted in a 79% loss of removal capacity when 9.6 mg of As (V) / g of WMOD zeolite was adsorbed. In the case of accelerated aging using an As (III) conc entrated solution, there was a 31% loss of the ability when 0126 mg of As (III) / g of WFE zeolite was adsorbed. As a result of the present invention, there are zeolitic adsorbents having a possible low cost and a potentially useful procedure for the treatment of groundwater in arid and semi-arid zones containing high concentrations of metalloids such as arsenic. This will reduce its contents to values lower than those established in the world health standards (0.01 mg / L), at short periods of time (= 5 mm). Depending on the As (V adsorption capacity presented by the WMOD, PMOD and the WFE zeolites, the methods and materials developed in the present invention are potentially useful for the treatment of groundwater contaminated with arsenic salts. By analogy of the latter with other oxyanions, its application may be extended to adsorption processes of selenium, antimony, tellurium, and chromium compounds, among other pollutants present in aqueous effluents. In addition, its applicati on might be extended to other areas both of scientific and technological interest such as the catalysis and ion exchange fields.