Potential valorisation of Protobind 1000 as adsorbent for Pb2+ AND Zn2+

Abstract

The adsorption of metal ions from increasing concentrations in aqueous solutions by modified straw lignin Protobind 1000 was studied. The effect of metallic ion concentrations (from 20.72 to 207.2 mg·L-1 for Pb2+ and from 6.538 to 65.38 mg·L-1 for Zn2+) and contact time (30, 60 and 90 minutes) were studied at pH = 6 and 200C. Langmuir and Freundlich isotherm equations were applied to assess equilibrium data and the kinetics of the adsorption processes were analysed using Lagergren pseudo first order and Ho&McKay pseudo second order models. The results show that the adsorption processes reached equilibrium after 90 minutes, but similar values were registered after 60 minutes. The Freundlich isotherm described the process better, denoting chemisorption with the formation of ion-lignin complex structures. The Ho&McKay model fit the adsorption data better with regression coefficients equal to 1 compared to the Lagergren model, where the regression factors varied between 0.72 and 0.95. For the maximum concentration of lead solution and the longest adsorption time of 90 minutes, the Ho&McKay model predicted an equilibrium capacity qe of 13.1406 mg·g-1 compared to the 13.1398 mg·g-1 obtained. For zinc adsorption, the same maximum concentration and time were considered, and the pseudo-second order model predicted a qe of 12.6743 mg·g-1 compared to the obtained value of 12.6714 mg·g-1. The uptake of lead was greater on 0.15 g of adsorbent (a maximum of 27.23 mg·g-1) than the zinc uptake (a maximum of 8.28 mg·g-1), for all analysed concentrations.