Complexation and sorption studies of Co(II) with γ-alumina-bound fulvic acid: effect of pH, ionic strength, fulvic acid and alumina concentration

Humus Acids in the Digested Sludge and Their Properties

Fulvic acids, alpha (α) humic acids and hymatomelanic acids were extracted digested sludge in two Cracow sewage treatment plants: Kujawy and Płaszów. Their elemental composition was examined and micropollution and ash content were determined. Based on the IR and UV-VIS spectrum, their similarities were determined with the occurring interactions with micropollution. Strong correlations between the acids coming from different sources depend on acid type and micropollution accompanying them, depending on concentration, influences to a specific extent their IR and UV-VIS spectra. Absorption analysis in infrared constitutes a simple method for characterizing fulvic and humic acids from wastewater treatment plants. The extracted fulvic acids were characterized by moderate maturity, while humus acids were well developed. In the fermentation process, the N bond increases together with the level of humification of the humus acid. The characteristics of the extracted humus acids comply with other humic substances presented in the literature. Quantitative analysis showed that digested sludge contains, on average: FA from 5.07 to 5.30 g/kg dry matter, αHA from 59.22 to 74.72 g/kg dry matter, HMA from 20.31 to 43.66 g/kg dry matter. It was thus demonstrated that wastewater treatment, in particular digested sludge, constitutes an attractive source of humus acids with a wide range of applications in numerous areas, such as agriculture, ecological rehabilitation, environmental protection, animal breeding, aquaculture, veterinary as well as medicine and is a precious source of soil fertilizers.

Complexation of lead and cadmium ions with humic acids from arctic peat soils

Humic acids (HAs) have many significant environmental and geochemical functions in soils, bottom sediments, and aquatic environments. Their interaction with toxic heavy metal ions affects their transport and bioavailability. This study suggests that binding of heavy metal ions to HAs could potentially help to develop strategies for recovering metal-contaminated soils and groundwater. This study is aimed at investigation of sorption properties of HA preparations from peat soils based on determining the kinetic and thermodynamic parameters of the sorption processes of Cd²⁺ and Pb²⁺ ions. Based on a model experiment, the binding ability of HAs of Hemic Folic Cryic Histosol to Cd²⁺ and Pb²⁺ ions was revealed. It is shown that during the initial stage (first 20 min for Cd²⁺ ions and 30 min for Pb²⁺ ions) the kinetics of the process of sorption of metal ions by suspended HA preparations is better described by pseudo-second order equation. This indicates the chemisorption mechanism and limiting contribution of chemical reaction. The kinetics sorption process within the Boyd - Adamson - Myers model is described with high precision for both ions during the whole experiment. This indicates the intra-diffusion limitation of the sorption process. The thermodynamic characteristics (the limiting sorption capacity, constant of sorption equilibrium, Gibbs free energy change, entropy change and enthalpy change of sorption) of the sorption process of selected heavy metal ions have been calculated. It was found that the limiting specific sorption of Pb²⁺ ions is almost an order of magnitude higher than that of Cd²⁺ ions and amounts to 0.16-0.29 mmol/dm³ and 0.0078-0.034 mmol/dm³, respectively. The sorption enthalpy variance of 48.4 kJ/mol for Cd²⁺ ions and 22.6 kJ/mol for Pb²⁺ ions indicate the endothermic nature of sorption on HA solid particles. It was shown that the limiting stage of sorption for Cd²⁺ and Pb²⁺ ions is ion diffusion to the sorbent, while chemisorption itself proceeds quite quickly. Values ΔS> -10 J/(mol ∙ K) indicate a dissociative sorption mechanism for both metals, i.e. non-sorbed ions in the solution are in a more ordered state than after sorption. The negative values of the Gibbs free energy change for Cd²⁺ and Pb²⁺ ions indicate that the interaction of ions with HA preparations from peat soils is a spontaneous process with a complex mechanism involving complexation and ion exchange processes.