Sustainable Acrocomia aculeata residue-based adsorbent for removal of ivermectin from aqueous solution: characterization, analysis of process variables and modelling

Description

Characterization of a biosorbent based on Acrocomia aculeata epicarp; a Central Composite Design for efficiency and amount adsorbed of ivermectin onto the biosorbent in relation to process temperature, medium pH and mass of adsorbent; isotherm and kinetics adjustment for the adsorption process.

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The epicarp was separated, washed and dried in vacuum stove at 80 ºC for 18 h. Then it was milled in micro mill Willye, model R-TE-648 and the resulting particles were classified in a Tyler system sieve. The samples pre-adsorption were analysed in natura and the posterior, after separation by centrifuge at 4000 rpm for 20 min, filtration in a 0,22 micrometre membrane filter and drying at 40 ºC for 24 h. The method for determination of point of zero charge used was by Uehara, 1981. The FTIR spectrum was obtained in a BOMEN Hartmann & Braun - The Michelson series MB-100 spectrometer, with spectral window 4000 – 500 cm-1, 4 cm-1resolution, 6 cycle accumulation and 0,2 cm/s scanning velocity. The samples were scattered in spectroscopic grade KBr and pressed at 6 ton with mechanical press. The samples for the SEM were fixed over brass stubs with double sided carbon tape and covered in gold by sputtering in Denton Vacuum, model Desk III equipment. The analysis was made in a Jeol, model JSM-6380 LV microscope. The thermal analysis was done in a STA 449 F3 Jupiter model (Netzsch), with N2 atmosphere, at 20 mL/min, from 25 to 900 ºC with 10 ºC/min step. The adsorbate solutions were prepared from solid ivermectin and deionized water. The solution stayed in an ultrasonic bath for an hour. The pH was adjusted with HCl and NaOH solutions and measured with Tecnal TEC-7 pHmeter. 25 mL of the solution was added to an Erlenmeyer flask with the mass of adsorbent. The adsorption experiments were made in batches in Tecnal orbital shaker, model TE-420, with 0,1 ºC precision temperature control, protection against UV rays, at 200 rpm in duplicates. At the end, the mixture was centrifuged at 4000 rpm for 20 minutes and the liquid phase was filtered on 0,22 micrometre microfilter. The experiment was done until thermodynamic equilibrium was reached. It was done concomitantly a medium in identical conditions without the adsorbate. The resulting sample was used as reference in the spectroscopic measures. The experimental design selected was a complete factorial with three variables and three repetitions on the central point, a total of 17 points. The variance analysis, statistical modelling, values prediction, Pareto charts, response surfaces and optimal conditions were generated on the software Statistica® 12.5 192.5. The parameters of each isotherm and kinetics model were estimated in the softwares OriginPro® 8 and Excel® 2013. The isotherm experiments conditions were the optimal conditions, until thermodynamic equilibrium, at 200 rpm. The initial adsorbate concentrations were from 10 to 100 g/L. The kinetic experiments conditions were the optimal conditions, at 200 rpm. The experiment duration was 3 h, the total volume of medium was 250 mL. 10 mL samples were taken from the medium after 3 minutes, after 10 minutes, then in 10 minutes intervals for an hour and in 30 minutes intervals for the remaining time.

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