Modified Polymeric Biosorbents from Rumex acetosella for the Removal of Heavy Metals in Wastewater

Abstract

The contamination of water resources by effluents from various industries often contains heavy metals, which cause irreversible damage to the environment and health. The objective was to evaluate different biosorbents from the weed Rumex acetosella to remove metal cations in wastewater. Drying, grinding and sieving of the stems was carried out to obtain the biomass, retaining the fractions of 250 to 500 µm and 500 to 750 µm, which served to obtain the biosorbents in natura (unmodified), acidic, alkaline, and mixed. Proximal analysis, PZC, TOC, removal capacity, influence of pH, functional groups, thermal analysis, structural characteristics, adsorption isotherms, and kinetic study were evaluated. The 250 µm mixed treatment was the one that presented the highest removal percentages, mainly due to the OH, NH, -C-H, COOH, and C-O functional groups achieving the removal of up to 96.14% of lead, 36.30% of zinc, 34.10% of cadmium and 32.50% of arsenic. For contact times of 120 min and an optimum pH of 5.0, a loss of cellulose mass of 59% at 328 °C and a change in the surface of the material were also observed, which allowed for obtaining a topography with greater chelating capacity, and the Langmuir and pseudo-second order models were better fitted to the adsorption data. The new biosorbents could be used in wastewater treatment economically and efficiently.

Keywords: Rumex acetosella; biosorption; heavy metals; metal removal; modified biomass.

Figure 1

Experimental flow diagram.

Figure 2

Plant material (a) and modified biosorbents from R. acetosella 250 µm (b) and 500 µm (c).

Figure 3

Point of zero charge in the fractions of 250 and 500 µm.

Figure 4

Principal component analysis in the removal of heavy metals, metal cations (a) and biosorbents (b).

Figure 5

Variation of heavy metal biosorption over time in the fractions of 250 and 500 µm.

Figure 6

Influence of pH on the removal of heavy metals for the 250 and 500 µm fractions of the mixed treatment T4.

Figure 7

Langmuir adsorption isotherms (a) and pseudo-second order model (b), for T4 (250 and 500 µm).

Figure 8

FTIR infrared spectra of the 250 and 500 µm fractions, before (a) and after (b) the biosorption process.

Figure 9

TG and DTG curves of the biosorbents obtained from the fractions of 250 and 500 µm.

Figure 10

Geometry of the obtained biosorbents (white bars indicate 250 and 500 µm).