Uso de microalgas para adsorção do corante rodamina B empregado na indústria de tingimento de ágata

Abstract

Rhodamine B (RhB) has been widely used in dyeing of semiprecious stones (agate), which are exported from the Southern Brazil, and in this dyeing process, colored effluents are generated. Then, the objective of this work was to carry out batch study use green microalgae Chlorella pyrenoidosa (CP) and commercial activated carbon (AC) and fixed bed study using the CP supported in sand for the removal of the rhodamine B dye. Initially the materials were characterized by Fourier Transform Infrared Spectrometry (FTIR), scanning electron microscopy (SEM), X-ray dispersive spectroscopy (EDX). For the microalgae was also carried out a test to verify biomass composition and for the commercial activated carbon.was made the X-ray diffraction (XRD), besides for both adsorbents the the point of zero charge was carried out. In the batch studies the effects of pH, contact time and temperature were evaluated. Adsorption kinetics were studied for the dye concentration range of 20 to 500 mg L-1, using pseudo-first-order, pseudo-second order and Elovich models. The equilibrium isotherms were analyzed by the Langmuir, Freundlich, Sips and Temkin models. In the fixed bed studies Chlorella pyrenoidosa was supported in sand and used as biosorbent material the effects of flow rate (Q = 1.6-18.4 mL min-1), initial concentration of dye (C0 = 32-368 mg L-1) and microalgae mass (M = 1.64-8.36 g) in the fixed bed column were evaluated in biosorption rupture curves, and these parameters were optimized by surface response (RSM) and desirability function. The compatibility of experimental data with dynamic models such as BDST, Thomas and Yoon-Nelson was investigated. In addition, bed regeneration was studied. In the batch tests the results show that in the initial concentration of dye was 100 mg L-1, the microalgae biomass and the activated carbon had the highest adsorption capacity, at pH 8.0 and 25 °C temperature. The time required to achieve equilibrium time was 120 minutes when the CP was used and 90 minutes when the activated carbon was used. The kinetic model that better fitted the experimental data, for the two adsorbents, was pseudo-second order, with an average relative error lesser than 2.4% and 5.3% for CP and CA respectively. The Sips isotherm presented the best performance, for the two adsorbents being the calculated values of the biosorption capacities of 63.14, 53.46 and 54.19 mg g-1 for the temperatures of 25, 35 and 45 ºC, respectively when using the microlagae and 147.58, 140.01 and 137.27 mg g-1 for the temperatures of 25, 35 and 45 ºC when the activated carbon was used, thus demonstrating that a temperature increase has a negative effect on the biosorption capacity. In the fixed bed studies the results showed that under optimal conditions the maximum column capacity was 48.7 mg g-1 and the removal percentage was 61.7% when the flow rate was 1.6 mL min-1, the initial concentration of RhB of 368.0 mg L-1 and amount of 5g microalgae. The dynamic models showed adjustments in the experimental data (R² = 0.9919), and could be applied to the prediction of column properties and breakthrough curves. Column regeneration was performed for five cycles of adsorption-elution using HCl solution (0.5 M) as the eluent. The results indicated that the adsorption with Chlorella pyrenoidosa and commercial activated carbon (AC) has great potential for the removal of rhodamine B from the dye effluents, in addition the fixed bed studies provide an important basis for future scale-up of fixed bed biosorption of RhB on microalgae supported on sand.