FINITE ELEMENT ANALYSIS OF THE DIFFUSION MODEL OF THE BIOCLOGGING OF THE GEOBARRIER

The distribution of an organic chemical and the filtration process in the soil which contains a thin geochemical barrier are considered. Microorganism colonies develop in the presence of organic chemicals in the soil which leads to the so-called phenomenon of bioclogging of the pore space. As a result, the conductivity characteristics of both the soil as a whole and the geochemical barrier change. Conjugation conditions as a component of the mathematical model of chemical filtration in the case of inhomogeneity of porous media and the presence of fine inclusions were modified for the case of bioclogging. The numerical solution of the corresponding nonlinear boundary value problem with modified conjugation conditions was found by the finite element method. The conditions of the existence of a generalized solution of the corresponding boundary value problem are indicated. The results on the theoretical accuracy of finite element solutions are presented. Differences in the value of pressure jumps at a thin geochemical barrier were analyzed for the case considered in the article and the classical case on a model example of filtration consolidation of the soil in the base of solid waste storage. The excess pressure in 600 days after the start of the process reaches 25 % of the initial value when taking into account the effect of bioclogging, while is only 6 % for the test case disregarding the specified effect.

Geochemical conditions of natural wetland and paddy fields in the Poyang Lake area, China

During the last several decades, wetlands are losing their ecological functions due to increasing anthropogenic loads. One of these functions is the ability to bind elements forming geochemical barriers. The research aimed to study the geochemical conditions of natural wetlands and flooded paddy fields (artificial wetlands) in the Ganjiang River basin to trace geochemical barriers. The research approach was based on a comprehensive analysis of water and aqueous extracts from bottom sediments and paddy soils, including chemical and mineral composition. The samples were collected in November 2019, during the dry season at the end of harvesting. Chemical analysis was performed using standard methods for natural substances: titrimetry, photometry, ionic chromatography, high-temperature oxidation, ICP-MS, and ICP-AES. The mineral composition of the soils and sediments was determined by XRD. It was found that the main physicochemical characteristics (TDS, pH, main component concentrations) of the natural wetland water correspond to the surface water of the study area, whereas the irrigation water is similar to shallow groundwater. The content of trace elements in the irrigation water is higher than in the natural wetland water. Generally, the trace element composition of the natural wetland water corresponds to the geochemical background of the study area. Analysis of the mineral and chemical composition of the paddy soils and sediments indicates the geochemical barriers that accumulate a wide range of elements. In the natural wetland, the geochemical barrier is likely associated with a decrease in oxygen content and advective transport rate in the sediments, whereas in the paddy fields, the precipitation of clay minerals in the soil profile forms the geochemical barrier related to a decrease in filtration properties and advection–diffusion transport. Graphic abstract

Unaccounted Environmental Risk of Fuel Filling Stations in the City

The statistically significant geochemical dependences of the dynamic behavior of petroleum products in urban soils in the fuel filling station zone are considered, the areal of their distribution are determined. The techniques used make it possible not only to identify laterally manmade modules of environmental hazard (laterally module) when oil products come from fuel filling stations, but also to determine additional factors of unaccounted environmental risk, for example, the process of accumulation of heavy metals in the soil profile in excess of the standards on the resulting geochemical barrier in the form of oil products. The risk assessment of oil product supply facilities should be carried out taking into account the specifics of the distribution of toxicants in technogenically altered soils.

An experimental study of sorption properties of natural zeolite-containing rocks and their ability for purification of aquatic solutions contaminated with Ni and Zn

<p>Sorption parameters of natural zeolite-containing tripolite from the Khotynetsky deposit (Russia, Oryol region) were studied in a series of experiments to evaluate possibility of its usage as a geochemical barrier for teсhnogenic Ni<sup>2+</sup> and Zn<sup>2+</sup> contaminating soils and ground waters. <br>Firstly, the tripolite total ion-exchange capacity was established by its saturation with ammonium ion and evaluating its content in the initial and ammonium forms with the help of X-ray fluorescence method. Secondly, the kinetic characteristics, namely the time necessary to reach the equilibrium state of the rock-water system containing Ni<sup>2+</sup> and Zn<sup>2+</sup> ions were determined in batch experiments using the method of "limited volume". The latter experiment was conducted using 0.5 g tripolite with 250 ml model solutions simulating natural river water (0.003 н CaCl<sub>2</sub>) and filtration water from solid domestic waste landfill (0.06 н CaCl<sub>2</sub>) and containing  2 mg/l Ni<sup>2+</sup> and  Zn<sup>2+</sup>. The time of contact between the sorbent and the model solution varied from 2 hours to 21 days. Thirdly, basing on reference data on the real content of heavy metals in the filtrates of various landfills, an experiment on determination of the tripolite equilibrium exchange (and adsorption) capacity was carried out. The prepared model solutions in the latter experiment contained 2, 5, 7 and 10 mg/l of Ni<sup>2+</sup> and Zn<sup>2+</sup>. The amount of Ni<sup>2+</sup> and Zn<sup>2+  </sup>in solutions was determined by the ICP-AES.<br>According to the obtained results, the total ion-exchange capacity of the natural tripolite equaled to 1.18 mg-eq/g. The sorption isotherms based on kinetic experiments showed that equilibrium in the studied rock-solution system took place after 200 to 500 hours of interaction. Despite natural scattering of experimental points in the range of the used Ni<sup>2+</sup> and Zn<sup>2+</sup> concentrations in the third experiment which lasted 21 days, the sorption of the studied ions by the natural tripolite can be approximated by a linear isotherm, zinc being sorbed much better than nickel. The average values of distribution coefficients (Kd) obtained for 0.003 n CaCl<sub>2</sub> aquatic solution equaled to 2.7*103 ml/g for Ni<sup>2+</sup> and 6.7*103 ml/g for Zn<sup>2+</sup>.<br>Therefore, natural tripolite of the Khotinetsky deposit may well be used as a natural geochemical barrier for extraction of technogenic Ni<sup>2+</sup> and Zn<sup>2+</sup> from natural waters draining landfills and contaminated by these ions.</p><p> </p>

Serpentine-reached mining wastes as a geochemical barrier for the soil remediation under the ongoing Cu-Ni pollution in the Russian Arctic

<p>The main factors for the degradation of the ecosystems in the metal-polluted territories are soil toxicity, organic matter degradation and violation of macro-element cycles. Heavily contaminated soils lose their ability to maintain sustainable vegetation, which leads to the formation of industrial barrens as the final stage of plant cover digression, where the vegetation cover is less than 10%. The deposition of metal mobile compounds into an insoluble form by alkaline sorbents is one of the most effective remediation techniques in situ. Technosol engineering is a trigger for the beginning of plant and soil cover development and the recovery succession under high pollution with metals compounds.</p><p>Field experiment of remediation using three types of serpentine mining wastes, expanded vermiculite and grass seeds mixture was laid down in 2010-2013 in the impact zone of the copper-nickel ore processing enterprise on the Kola peninsula (northern Europe) beyond the Arctic Circle at two sites with podzol and peat soil. The results obtained in 2019 showed that the immobilization effect was strengthened by high pH inherited from the alkaline wastes making Technosols a geochemical barrier. For the first 5-8 years of the experiment, the Technosol upper layers primary consisted of serpentine minerals, accumulated more than 1 g·kg-1 Ni and 0.1 g·kg<sup>-1</sup> Cu which are constantly deposited from the atmosphere as a result of the Cu-Ni enterprise activity. They also affected the underlying soil and neutralized the most toxic water-soluble and exchangeable fractions of Cu and Ni. Grass growing and litter deposition (in total 4.5-6 kg·m<sup>-2</sup>) during the experiment term led to the accumulation of organic carbon by serpentine minerals about 1.5%. Organic matter accumulation also played a significant role in metal binding by upper Technosol layers. Summarily, the remediation technology through the use of serpentine-reached mining wastes bound metals emitted by smelter into insoluble forms, reduced the toxicity of water-soluble and exchangeable fractions of heavy metals and promoted the sustainable development of plant cover.</p><p>Research was carried out with the support of the Russian Science Foundation grant 19-77-00077.</p><p> </p>