Using agrifood residues with complexing functional groups in the removal of metals from polluted waters

Resumen

A novel alternative to reuse and valorise the broccoli stalks (considered as agrifood industrialresidue) as a low-cost biosorbent for the removal of Pb(II) ions from polluted water has beenproposed. Lignocellulosic biomasses as broccoli stalks are attractive as potential sorbentsfor the removal of heavy metal (as Pb(II)) from aqueous media due to its active functionalgroups,1 which purvey promising sorption sites. Experimental conditions involved in thebiosorption process such as pH, amount and particle size of sorbent, and biomasspretreatment were optimised. The biosorption capacity was studied in batch scale for 8hours, measuring the metal ion concentration in solutions by atomic spectroscopy. Theoptimal removal percentage of Pb(II) was obtained at pH 4.8 using 10 g/L of biosorbent. Aremoval of 88.1±0.2 % for 1mmol/L Pb(II) was achieved and a good linear behaviour in thestudied range of 0.25-1.5 mM Pb(II). The equilibrium sorption data were studied by fitting toLangmuir, Freundlich and Temkin adsorption isotherm equations; Temkin model showed thebest fit (R2=0.9997). The kinetic of the Pb(II) sorption process of Pb(II) followed a pseudosecond order model (R2=0.9999), suggesting the chemisorption as the controllingmechanism. Thermodynamic parameters indicated the endothermic nature of the process.The surface of biomass was characterised by the Boehm methodology being predominantlyacid, with a higher content of carboxylic groups (1.22 mmol/g) than phenolic or lactonicfunctional groups. As conclusion, biosorption with broccoli stalks has proved to be anexcellent option for the removal of Pb(II) from polluted waters.