Potencialidade adsorvente da zeólita A derivada de rejeito de caulim na remoção de corantes

Abstract

In the States of Pará and Amapá are the largest Brazilian reserves of kaolin. The process of beneficiation of this material generates a significant volume of waste, this is kaolin that is out of the specifications for paper coverage and ends up becoming an environmental liability, since large areas are required to be deposited. This reject consists mainly of the kaolinite clay that presents Si and Al in a ratio of 1: 1, ideal to be used as raw material in the synthesis of zeolites. Zeolite A is a microporous synthetic aluminosilicate, easily synthesized from kaolin waste, making it a low cost and effective material to remove contaminants present in the effluents, such as dyes, besides having a high degree of selectivity and other characteristics that make it an excellent adsorbent. Among the most used processes in the dye removal is the adsorption, because it has several advantages such as: low cost, high removal rates and the possibility of adsorbent recovery. The work methodology was carried out in four stages: 1) Zeolite A synthesis: the Tube Press kaolin was used as starting material from the company located in the Capim-PA River, which was subsequently calcined at 700 ° C for 2h, solution of NaOH (5 mols L-1) and distilled water. They were kept in a reactor for 2 h at 95 ° C under stirring. After the synthesis the material was washed to pH = 7 and dried. Both the starting material and the products were identified and characterized by DRX, MEV, DTA-TGA and granulometric analysis. 2) The adsorption study was performed with AM and VC dye solution at concentrations of 2-26mg L-1. The equilibrium, adsorption kinetics and thermodynamics were obtained. The tests were done in a batch system and the solutions after adsorption were analyzed in UV-Visible spectrophotometer, using λ = 585nm for AM and λ = 665nm for VC. 3) Zeolite A regeneration was performed with 50 ml of the dye solution in the concentration 10 mg L -1 and 150 mg zeolite A. After 24 h the suspension was centrifuged, the supernatant analyzed and the solid dried and then calcined at 650 °C for 2 h to a five-fold cycle. 4) Desorption study: 50 ml of AM and VC dye solution at 10 mg L-1 and 150 mg zeolite A, after adsorption of 24 h the solid was separated by centrifugation and the water and methanol solvents were subsequently added in five proportions to give the initial volume of 50 ml and kept under stirring for 24 hours and after analysis of the supernatant in UV-Visible spectrophotometer. In the results of the adsorption equilibrium, the percentage of adsorption decreases with increasing concentration, as more dye molecules are incorporated into the adsorbent, reducing the area and the available active sites. The maximum adsorption capacity at equilibrium for MA was 5.1 mg g-1 and for the CV of 14.09 mg g-1, in this way the equilibrium adsorption capacity was higher for the CV as compared to the MA. The mathematical model that best fit the experimental data of AM equilibrium was the Sips isotherm that combines characteristics of the Langmuir and Freudlich isotherms, whereas for the VC dye the best model is that of Freudlich suggesting that adsorption occurs in multilayers. The adsorption kinetics of AM and VC were adjusted to the pseudo second order model. The thermodynamics of adsorption of AM at temperatures of 30 °C to 70 °C is a spontaneous process, favored at higher temperatures. The thermal regeneration of zeolite A after 5 cycles of regeneration had a loss in the efficiency of the AM adsorption in 7% and 3% for the CV, indicating the possibility of reuse of the adsorbent. Desorption with the 50% mixture of each solvent showed the best results.