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Colloid and colloid-facilitated solute transport have been identified as major environmental issues in the past few decades. Several field and laboratory-scale experiments have confirmed the rapid migration of radionuclides, heavy metals, pharmaceuticals, and pesticides adsorbed by colloids present in the subsurface aquifer system. This study deals with fundamental mechanisms of colloid mobilization and the principle mathematical relationship describing the various modifications of colloid transport like attachment–detachment, size exclusion, and air–water interfacial area. The effect of the size exclusion mechanism on the movement of colloids in the subsurface system is represented pictorially through a numerical model. In addition, the effect of surface potential and Hemakar constant on the interactions of colloidal particles are also elaborated. This article investigates the studies in this area through the bibliometric analysis of the articles extracted from the Scopus database from 1984 to 2021. The network and density distribution plots provide the recent development and trend of research in this field. The effect of water saturation and initial concentration of colloids attached to solid–water interface on release and mass recovery of colloidal particles under cycles of imbibition and drainage need to be interpreted experimentally. Numerical models considering attachment of mobile colloids at air–water interface and air–water–solid contact line under transient flow fields should be incorporated to study the complex migration characteristics of the colloidal particles present in the subsurface ecosystem during infiltration and water table fluctuations. Underestimating the rapid migration of contaminants attached to mobile colloids imparts potential risk of vadose zone and groundwater contamination. [ABSTRACT FROM AUTHOR]

Changing the composition of a precursors mixture is a powerful tool to tune the structure and properties of carbonaceous nanoparticles synthesized via the solvothermal route. We have addressed the influence of the ratio of urea or thiourea to citric acid during their solvothermal treatment in dimethylformamide on the optical and sensing properties of the obtained colloidal product. It has been found that the urea-derived products are more diverse in comparison with the thiourea-based ones. The excitation-dependent fluorescence of the products and their sensitivity to mercury(II) ions have been investigated; one to three types of fluorophores have been observed in the products depending on the composition. The nanoparticles prepared in excess of urea have been found more sensitive to the heavy metal, with the sensitivity of the long-wave emission band being superior. [ABSTRACT FROM AUTHOR]

The soil contaminated with heavy metals requires special attention due to its adverse effects on health of human and animals. The effects of simulated acid rain with different pH values on transport of heavy metal in contaminated soil of Phyllostachys pubescens forest were studied by indoor leaching column test. The results revealed that particle size of soil was mainly concentrated in range of more than 50 μm. The content of heavy metals in particles less than 50 μm was relatively high. The Pb and Zn were mainly adsorbed on colloidal particles and were transported during simulated acid rain. The release of Fe and Al increased the release of particulate matter in soil leaching solution. The mobility of Zn was increased at low pH. [ABSTRACT FROM AUTHOR]

Abstract The Río Tinto mining area provides ideal conditions for studying the role of colloidal particles in concentrating. All the elements are present in higher concentrations respect to their content in common natural waters. 234U/238U activity ratio ranges between 2.286 ± 0.149 and 2.531 ± 0.151. Concentration of Fe and Al are in the order of 104–103 mg/L; Co, Zn and Cu values are three times lower than Fe and Al, but still much greater than in natural waters; U reaches values up to 40.73 μg/L. To evaluate the partitioning of these elements into the colloidal fraction, ultrafiltration (UF) experiments were made. A permeation model describing the relationship between concentration of the elements or isotopes in the permeate solution and the concentration factor (CF) was calculated. Experiments were carried out using CF from 1.5 to 25.0. The behaviour of investigated heavy metals and U can be predicted by a permeation model that provides similar permeation coefficient (P c) for all of them (P c = 0.95–0.97 for 50 kDa, P c = 0.86–0.88 for 10 kDa, and P c = 0.80–0.86 for 3 kDa). Retention for all the investigated elements occurs, resulting in up to 23% of the element associated to the 3 kDa colloidal fraction. The increase in U and heavy metals concentrations in the retentate fraction with the increasing CF is due to the retention of the colloidal fraction. The colloidal abundance of related metals increased with decreasing membrane MWCO even though the difference is small between 3 and 10 kDa fraction for some metals Characterization of colloidal material is needed to better understand the state of play in this context. Highlights • Partitioning of U and selected heavy metals in dissolved and colloidal fractions in AMD conditions were examined. • UF with distinct MWCO was used and a permeation model to quantify the behaviour of U and selected metals was applied. • Metal concentrations much higher than those in natural waters were found and high 234U/238U in the water samples were observed. • Little colloidal metals in the size fraction 3–10 kDa are present, likely due to the strong acidic conditions. • Low concentrations of colloidal U in the study area were measured. [ABSTRACT FROM AUTHOR]

Exposed mine tailing wastes with considerable heavy metals can release hazardous colloidal particles into soil under transient chemical and physical conditions. Two-layered packed columns with tailings above and soils below were established to investigate mobilization and transport of colloidal particles from metal-rich mine tailings into soil under transient infiltration ionic strength (IS: 100, 20, 2 mM) and flow rate (FR: 20.7, 41, and 62.3 mm h), with Cu and Pb as representatives of the heavy metals. Results show that the tailing particles within the colloidal size (below 2 μm) were released from the columns. A step-decrease in infiltration IS and FR enhanced, whereas a step-increase in the IS and FR restrained the release of tailing particles from the column. The effects of step-changing FR were unexpected due to the small size of the released tailing particles (220-342 nm, being not sensitive to hydrodynamic shear force), the diffusion-controlled particle release process and the relatively compact pore structure. The tailing particles present in the solution with tested IS were found negatively charged and more stable than soil particles, which provides favorable conditions for tailing particles to be transported over a long distance in the soil. The mobilization and transport of Cu and Pb from the tailings into soil were mediated by the tailing particles. Therefore, the inherent toxic tailing particles could be considerably introduced into soil under certain conditions (IS reduction or FR decrease), which may result in serious environmental pollution. [ABSTRACT FROM AUTHOR]