Avaliação do emprego do pseudocaule da bananeira (Musa paradisiaca) na remoção de Cr(III) em solução aquosa

Abstract

The search for balance between economic development and environmental saving has been directing several academic researches and demanding from the society less polluting attitudes. The recycling or reuse of natural raw materials has become an alternative to the use of synthetic compounds employed with the same purposes. In this sense, appear the natural adsorbents or biosorbents, which hold characteristics such as high capacity for removal of effluents and elevated availability added to a low cost. The banana (Musa sp.) is the most traded fruit in the world. After maturation and harvesting the bunch of bananas, the pseudo-stem dies (or is cut), leading eventually to a new pseudo-stem, and thus bringing a new "cluster" of pseudo fruit. Nearly 70% of pseudo-stem’s composition consists of lignin, cellulose and hemicellulose, which have adsorptive sites such as carboxyl, carbonyl and hydroxyl, able to participate in the various mechanisms involved in biosorption. The purpose of this study is to evaluate the removal of Cr(III), contaminant present in the effluent of electroplating industry, employing the pseudo-stem of banana (Musa paradisiaca) as biosorbent. The characterization was carried out on both samples from biomass: natural fresh pseudo-stem and pseudo-stem from heat treatment, being kept immersed in water at boiling point for one hour. The point of zero charge pHzpc obtained was the value of 5,7 for both samples. Through F.T.I.R. analysis, no differences were observed between the organic functional groups present in the fresh biomass and the one treated. The results about the concentrations of nitrogen, phosphorus and potassium, to the fresh sample were 0,19, 0,27 and 2,9% w/w, respectively, while for the pseudo-stem previously treated were 0,25, 0,51 and 3,8% w/w, respectively. The concentrations of hemicellulose, cellulose and lignin for the pseudo without heat treatment were 12,35, 13,32 and 19,47% w/w, respectively, and the pseudo treated, concentrations were 18,2, 10,53 and 23,03% w/w. The experiments were directed by an experimental design. The one assumed for this work was the Complete Factorial Design. The parameters evaluated were pH, initial metal concentration and biosorbent mass increment. O average pH ranged from 1 to 12 being considered a significative factor. Due to high pH values, the optimal regions for removal viewed on the surfaces generated by Statistica®, could not be attributed only to the biosorption phenomena, in this conditions the great of the metal was found precipitated. The mass of biosorbent ranged from 100 to 300 mg, and was a significative variable to the process, meanwhile the initial concentration of Cr(III) ranged from 0,5 to 100 mg.L-1. The sample of pseudo-stem treated presented as the best biosorbent in this study, compared to the pseudo-stem fresh. The models of Langmuir and Freundlich isotherms were tested for biosorption. The regression coefficients obtained were 0,972 and 0,946, respectively. Thus, the equation that best modeled the experiment was the Langmuir. Even reaching values of 90,5%, removals did not achieve the emission limits of Cr(III) established by CONAMA Resolution 357/ Fresh water, brackish and saline.