The effect of carbonization temperature on textural properties of sewage sludge-derived biochars as potential adsorbents.

This article presents ways of recovering waste in the form of anaerobically digested and dried sewage sludge (average humidity approx. 6 wt%) by carbonization at various temperatures in the range of 400-900 °C. The resulting products, biochars, are investigated in terms of yield, surface properties and Raman spectra analysis. The sorption capacity of biochars differs depending on the carbonization temperature. The experimental amount of adsorbed CO2 slowly increases with the carbonization temperature from 0.212 mmol/g at 400 °C to the highest value of 0.415 mmol/g, which is achieved at 900 °C by slow carbonization at a rate of 10 °C/min. Additionally, there is a strong positive dependence of the adsorption capacity on the micropore volume. Higher carbonization temperatures support the powerful formation of micropores and improve their sorption capacity.

Biochar as an effective material for acetone sorption and the effect of surface area on the mechanism of sorption.

Walnut shells and apricot pits were used to produce non-activated, air-activated and steam-activated biochar. The specific surface area decreased in the order steam-activated (500-727 m 2.g-1), air-activated (59-514 m2.g-1) and non-activated biochars (1.71-236 m2.g-1). The results indicated that water steam created a multi-layer block structure with a well-developed porous structure, especially at 900 °C, while activation with air resulted in a more fragmented structure with a higher amount of coarse pores, leading to lower specific surface values. Acetone sorption experiments were performed in order to determine the acetone sorption capacity and to evaluate the acetone sorption kinetics of the biochars, as well as to identify the possible mechanism of sorption. The maximum sorption capacity estimated from the adsorption isotherms up to a relative pressure of 0.95 ranged from 60.3 to 277.3 mg g-1, and was highest in the steam-activated biochar with the largest surface area. The acetone adsorption isotherms were fitted with different adsorption models, where the Fritz-Schlunder model showed the best fitting results. The adsorption kinetics was evaluated using two kinetics models - pseudo first order and pseudo second order. The results indicated that the biochars with a large surface area exhibited physical sorption through van der Waals forces as the dominant mechanism, while acetone sorption on samples with a smaller surface area can be attributed to a mixed dual sorption mechanism, which combines physical sorption and chemisorption on oxygen functional groups. The perfect reusability of the biochars was confirmed by four consecutive adsorption-desorption cycles.

Structural changes in amber due to uranium mineralization.

The presence of uranium, with a bulk mass fraction of about 1.5 wt% and radiolytic alterations are a feature of Cenomanian amber from Krizany, at the northeastern edge of the North Bohemian Cretaceous uranium ore district. Pores and microcracks in the amber were filled with a mineral admixture, mainly in the form of Zr-Y-REE enriched uraninite. As a result of radiolytic alterations due to the presence of uranium, structural changes were observed in the Krizany amber in comparison with a reference amber from Nové Strasecí in central Bohemia; this was of similar age and botanical origin but did not contain elevated levels of uranium. Structural changes involved an increase in aromaticity due to dehydroaromatization of aliphatic cyclic hydrocarbons, loss of oxygen functional groups, an increase in the degree of polymerization, crosslinking of CC bonds, formation of a three-dimensional hydrocarbon network in the bulk organic matrix, and carbonization of the organic matrix around the uraninite infill.