Alessio Cibati: The potential use of biochars as metal adsorbent for the remediation of wastewater

STSM at SIMBIOS Center, Abertay University in Dundee (UK)

Under the supervision of Dr. Bente Foereid, Alessio Cibati investigated the suitability of biochars produced at different pyrolysis temperatures and from different feedstock to adsorb metals (Cu and Zn) contaminants. The adsorption capacity of biochar produced from Miscanthus x giganteus was tested under varying fundamental parameters (pH, size of particle, effect of chemical activation, metal concentration and pyrolysis temperature).

pH, size of particle, effect of chemical activation, metal concentration and pyrolysis temperature play key roles in the adsorption mechanism.

The aims of this work were: (I) to quantify the adsorption capacity of biochars, and (II) relate the adsorption to the physical and chemical characteristic of biochar, (III) to quantify how this is affected by the chemical activation and pyrolysis temperature.

Miscanthus x giganteus  biochar showed to be an economic and environmental-friendly method to adsorb metals as copper and zinc from aqueous solution. Biochar's particle size, played an important role in terms of metals removal capacity of biochar; pyrolysis temperature also influenced positively the adsorption capacity, in fact biochar pyrolysed at higher temperature showed higher adsorption capacity for both metals investigated; Preliminary potentiometric titration tests suggested that the biochar is an heterogeneous material that shows two acid sites: carboxyl groups and phosphate groups.

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Figure 1. X-ray CT scan images of BC600 (fig. A) and raw Miscanthus biomass (fig. B)

The effect of pyrolysis temperature is clearly evident on the structure of biochar. Biochar pyrolyzed at 600°C (fig. A) showed a collapse of the structure starting from the inner part toward the outer part. This could be due to the higher temperature that causes the formation of gases that tend to escape toward the external part causing fractures of the structure. This supposition needs to be confirmed by further analysis, also comparing BC600 with BC350 to see if at lower pyrolysis temperature occurs a collapse of the structure as observed for BC600. In fig. B is reported an image of Miscanthus raw biomass.

Alessio personally considers this STSM as a very positive experience that allowed him to acquire new knowledge about the properties of biochar in the field of wastewater remediation.