ABSTRACT
The progressive influx of engineered nanoparticles (ENPs) into the soil matrix catalyses a fundamental transformation in the equilibrium dynamics between the soil and the edaphic solution. This all-encompassing investigation is geared towards unravelling the implications of an array of ENP types, diverse dosages and varying incubation durations on the kinetics governing Cd2+ sorption within Ultisol soils. These soils have been subjected to detailed characterizations probing their textural and physicochemical attributes in conjunction with an exhaustive exploration of ENP composition, structure and morphology. To decipher the intricate nuances of kinetics, discrete segments of Ultisol soils were subjected to isolated systems involving ENP dosages of 20 and 500 mg ENPs·kg-1 (AgNPs, CuNPs and FeNPs) across intervals of 1, 3 and 6 months. The comprehensive kinetic parameters were unveiled by applying the pseudo-first-order and pseudo-second-order models. At the same time, the underlying sorption mechanisms were studied via the intra-particle diffusion model. This study underscores the substantial impact of this substrate on the kinetic behaviours of contaminants such as Cd, emphasizing the need for its consideration in soil-linked economic activities and regulatory frameworks to optimize resource management.
ABSTRACT
Nanoscale zero-valent iron (NZVI) and NZVI supported onto montmorillonite (NZVI-Mt) were synthetized and used in this study to remove SeVI and AsV from water in mono- and binary-adsorbate systems. The adsorption kinetics and isotherm data for SeVI and AsV were adequately described by the pseudo-second-order (PSO) (r2>0.94) and Freundlich (r2>0.93) equations. Results from scanning electron microscopy showed that the dimension of the NZVI immobilized on the Mt was smaller than pure NZVI. Using 0.05 g of adsorbent and an initial 200 mg L-1 AsV and SeVI concentration, the maximum adsorption capacity (qmax) and partition coefficient (PC) for AsV on NZVI-Mt in monocomponent system were 54.75 mg g-1 and 0.065 mg g-1·µM-1, which dropped respectively to 49.91 mg g-1 and 0.055 mg g-1·µM-1 under competitive system. For SeVI adsorption on NZVI-Mt in monocomponent system, qmax and PC were 28.63 mg g-1 and 0.024 mg g-1·µM-1, respectively. Values of qmax and PC were higher for NZVI-Mt than NZVI and montmorillonite, indicating that the nanocomposite contained greater adsorption sites for removing both oxyanions, but with a marked preference for AsV. Future research should evaluate the effect of different operational variables on the removal efficiency of both oxyanions by NZVI-Mt.
ABSTRACT
The frequent use of phosphorus (P) fertilisers accompanied by nitrogen and potassium sources may lead to a serious long-term environmental issue because of the presence of potentially hazardous trace metals (TM) in P fertilisers and unknown effects on the TM chemical fractions in agricultural soils. A 16-month-long column experiment was conducted to investigate the mobility and chemical forms of Cd, Cu, Cr, Ni, and Zn introduced into a Mollisol and an Andisol through surface incorporation (0-2 cm) of triple superphosphate (TSP) fertiliser. The effects of urea and potassium chloride (KCl) applications were investigated as well. After 15 cycles of 300-mm irrigation, TSP addition increased the 4 M HNO3 extractable TM concentration in the upper (0-5 cm) section of soils. Beyond this depth, metals showed no significant mobility, with minimal leaching losses (< 1.9%, 25-cm depth). The TM chemical forms in the 0-5 cm section were significantly (p < 0.01) affected by the soil type and fertilisers addition. Cadmium, Ni, and Zn were the elements which appeared in a larger proportion (up to 30%) in the most labile fraction (KNO3 extractable) in fertilised soils. The impact of urea depended on the nitrification-related changes in soil pH, while fertilisation with KCl tended to increase the KNO3 fraction of most metals probably due to K+ exchange reactions. Chromium remained minimally affected by the urea and KCl applications since this contaminant is strongly bound to the less labile solid phases. The low mobility of TM was governed mainly by their interaction with the solid phases rather than by their speciation at soil pH. The mass balance showed that the geochemical processes underwent in time by the P fertiliser increased the amount of TM extracted by the chemical fractionation scheme, therefore the reaction period of TSP with soil particles should be taken into account for evaluating TM availability. Long-term soil fertilisation could inadvertently contribute to an increased concentration and availability of these P fertilisers-born contaminants in the cultivated layer of acidic soils.
