Evaluación de la eficiencia de la borra de café como material bioadsorbente para la remoción de cromo hexavalente (Cr+6)

Abstract

Adsorption is a widely used method for treating dissolved contaminants. Various agro-industrial wastes have been explored as potential adsorbents, showing high efficiency in the elimination of pollutants. In order to evaluate the removal efficiency and the adsorption kinetics of the previously treated coffee grounds (BC) for the adsorption of the hexavalent chromium ion (Cr+6) obtained from aqueous solutions of potassium dichromate (K2Cr2O7), A methodological design was proposed that allows to control a batch scale the independent variables agitation, pH, grain size of the BC, temperature and taking as factors the amount of BC, the initial concentration and the influencing contact time of the dependent variable expressed in removal percentage and in the amount of solute retained in the adsorbent at equilibrium (mg / g) (qe). The ANOVA was used as a statistical method of analysis of variance, obtaining a p-value less than 0.05 for the three factors, indicating that they are significantly different from zero with a confidence level of 95.0%, which indicates that the alternative hypothesis stipulated in the project. The highest removal percentages were 83.17-99.76% for concentrations of 10 to 70 mg / L of Cr + 6 with a contact time between 300 minutes to 540 minutes and maintaining a quantity of coffee of 1.5 g of BC. To evaluate the adsorption equilibrium, two mathematical models were applied, the Langmuir and Freundlich isotherm, resulting in a correlation coefficient of 0.9931 and 0.9954 respectively and a maximum bioadsorption capacity (qmax) of 66.19 mg / L, the calculation of the parameters of the isotherms and the graphic analysis of these allowed to explain that the type of adsorption phenomenon is physical (physisorption) and that it occurs in the form of multilayers without interaction between the molecules; This characteristic is due to the high porosity of the BC material close to 99% value that was obtained in the characterization of the adsorbent material.