Removal and recovery of heavy metals from soil with sodium alginate coated FeSSi nanocomposites in a leaching process

Rapidly reducing cadmium from contaminated farmland soil by novel magnetic recyclable Fe3O4/mercapto-functionalized attapulgite beads

Reducing cadmium (Cd) content from contaminated farmland soils remains a major challenge due to the difficulty in separating commonly used adsorbents from soils. This study synthesized novel millimeter-sized magnetic Fe3O4/mercapto-functionalized attapulgite beads (MFBs) through a facile one-step gelation process incorporating alginate. The MFBs inherit the environmental stability of alginate and enhance its mechanical strength by hybridizing Fe3O4 and clay mineral components. MFBs can be easily separated from flooded soils by magnets. When applied to 12 Cd-polluted paddy soils and 14 Cd-polluted upland soils, MFBs achieved Cd(II) removal rates ranging from 16.9% to 62.2% and 9.8%-54.6%, respectively, within a 12-h period. The MFBs predominantly targeted the exchangeable and acid soluble, and reducible fractions of Cd, with significantly enhanced removal efficiencies in paddy soils compared to upland soils. Notably, MFBs exhibited superior adsorption performance in soils with lower pH and organic matter (OM) content, where the bioavailability and mobility of Cd are heightened. The reduction of Cd content by MFBs is a sustainable and safe method, as it permanently removes the bioavailable Cd from soil, rather than temporarily reducing its bioavailability. The functional groups such as -SH, -OH, present in attapulgite and alginate of MFBs, played a crucial role in Cd(II) adsorption. Additionally, attapulgite and zeolite provided a porous matrix structure that further enhanced Cd(II) adsorption. The results of X-ray photoelectron spectroscopy suggested that both chemical precipitation and surface complexation contributed to Cd(II) removal. The MFBs maintained 87.6% Cd removal efficiency after 5 regeneration cycles. The surface of the MFBs exposed new adsorption sites and increased the specific surface area during multiple cycles with Cd-contaminated soil. This suggests that MFBs treatment with magnetic retrieval is a potentially effective pathway for the rapid removal of Cd from contaminated farmland soils.

New insights into the environmental application of hybrid nanoparticles in metal contaminated agroecosystem: A review

Heavy metals (HMs) contamination in agricultural soils is a major constraint to provide safe food to society. Cultivation of food crops on these soils, channels the HMs into the food chain and causes serious human health and socioeconomic problems. Multiple conventional and non-conventional remedial options are already in practice with variable success rates, but nanotechnology has proved its success due to higher efficiency. It also led the hypothesis to use hybrid nanoparticles (HNPs) with extended benefits to remediate the HMs and supplement nutrients to enhance the crop yield in the contaminated environments. Hybrid nanoparticles are defined as exclusive chemical conjugates of inorganic and/or organic nanomaterials that are combinations of two or more organic components, two or more inorganic components, or at least one of both types of components. HNPs of different elements like essential nutrients, beneficial nutrients and carbon-based nanoparticles are used for the remediation of metals contaminated soil and the production of metal free crops. Characterizing features of HNPs including particle size, surface area, reactivity, and solubility affect the efficacy of these HNPs in the contaminated environment. Hybrid nanoparticles have great potential to remove the HMs ions from soil solution and restrict their ingress into the root tissues. Furthermore, HNPs of essential nutrients not only compete with heavy metal uptake by plants but also fulfill the need of nutrients. This review provides a comprehensive overview of the challenges associated with application of HNPs in contaminated soils, environmental implications, their remediation ability, and factors affecting their dynamics in environmental matrices.

A review for recent advances on soil washing remediation technologies

Contaminated soils have caused serious harm to human health and the ecological environment due to the high toxicity of organic and inorganic pollutants, which has attracted extensive attention in recent years. Because of its low cost, simple operation and high efficiency, soil washing technology is widely used to permanently remove various pollutants in contaminated soils and is considered to be the most promising remediation technology. This review summarized the recent developments in the field of soil washing technology and discusses the application of conventional washing agents, advanced emerging washing agents, the recycling of washing effluents and the combination of soil washing and other remediation technologies. Overall, the findings provide a comprehensive understanding of soil washing technology and suggest some potential improvements from a scientific and practical point of view.

Natural Polymers and Their Nanocomposites Used for Environmental Applications

The aim of this review is to bring together the main natural polymer applications for environmental remediation, as a class of nexus materials with advanced properties that offer the opportunity of integration in single or simultaneous decontamination processes. By identifying the main natural polymers derived from agro-industrial sources or monomers converted by biotechnology into sustainable polymers, the paper offers the main performances identified in the literature for: (i) the treatment of water contaminated with heavy metals and emerging pollutants such as dyes and organics, (ii) the decontamination and remediation of soils, and (iii) the reduction in the number of suspended solids of a particulate matter (PM) type in the atmosphere. Because nanotechnology offers new horizons in materials science, nanocomposite tunable polymers are also studied and presented as promising materials in the context of developing sustainable and integrated products in society to ensure quality of life. As a class of future smart materials, the natural polymers and their nanocomposites are obtained from renewable resources, which are inexpensive materials with high surface area, porosity, and high adsorption properties due to their various functional groups. The information gathered in this review paper is based on the publications in the field from the last two decades. The future perspectives of these fascinating materials should take into account the scale-up, the toxicity of nanoparticles, and the competition with food production, as well as the environmental regulations.

Method and mechanism of chromium removal from soil: a systematic review

Heavy metal pollution has increasingly affected human life, and the treatment of heavy metal pollution, especially chromium pollution, is still a major problem in the field of environmental governance. As a commonly used industrial metal, chromium can easily enter the environment with improperly treated industrial waste or wastewater, then pollute soil and water sources, and eventually accumulate in the human body through the food chain. Many countries and regions in the world are threatened by soil chromium pollution, resulting in the occurrence of cancer and a variety of metabolic diseases. However, as a serious threat to agriculture, food, and human health. Notwithstanding, there are limited latest and systematic review on the removal methods, mechanisms, and effects of soil chromium pollution in recent years. Hence, this article outlines some of the methods and mechanisms for the removal of chromium in soil, including physical, chemical, biological, and biochar methods, which provide a reference for the treatment and research on soil chromium pollution drawn from existing publications.

Simultaneous removal of nitrate and diethyl phthalate using a novel sponge-based biocarrier combined modified walnut shell biochar with Fe3O4 in the immobilized bioreactor

A novel biological carrier combining sponge and modified walnut shell biochar with Fe₃O₄ (MWSB@Fe₃O₄) was fabricated to achieve simultaneous removal of nitrate and diethyl phthalate (DEP). The optimal reaction conditions of the immobilized bioreactor were: carbon to nitrogen (C/N) ratio of 1.5, Fe²⁺ concentration of 20 mg L^-1, and hydraulic retention time (HRT) of 8 h. Under the optimal conditions and DEP concentration of 800 μg L^-1, the highest removal efficiency of DEP and nitrate in the immobilized bioreactor with the novel biological carrier were 67.87% and 83.97% (68.43 μg L^-1 h^-1 and 1.71 mg L^-1 h^-1), respectively. Scanning electron microscopy (SEM) showed that the novel biological carrier in this study carried more bio-sediments which is closely related to the denitrification efficiency. The gas chromatography (GC) data showed that the nitrogen production of the immobilized bioreactor (99.85%) was higher than that of another experimental group (97.84%). Fluorescence excitation-emission matrix (EEM) and Fourier transform infrared spectrometer (FTIR) indicated the immobilized bioreactor emerged more extracellular polymeric substances (EPS) which was related to favourable biological stability under the DEP environment. Moreover, according to high-throughput sequencing data, the Zoogloea sp. L2 responsible for iron-reduction and denitrification was the main strain in this immobilized bioreactor.

Converting loess into zeolite for heavy metal polluted soil remediation based on "soil for soil-remediation" strategy

Both soil erosion and soil contamination pose critical environmental threats to the Chinese Loess Plateau (CLP). Green, efficient and feasible remediation technologies are highly demanded to meet these challenges. Herein we propose a unique "soil for soil-remediation" strategy to remediate the heavy metal polluted soil in CLP by converting loess into zeolite for the first time. With a simple template-free route, the natural loess can be converted into cancrinite (CAN) type of zeolite. A highly crystalline CAN was obtained via hydrothermal treatment at 240 ^oC for 48 h, with a precursor alkalinity of Na/(Si+Al)> 2.0. The as-synthesized CAN zeolite exhibits excellent remediation performance for Pb(II) and Cu(II) polluted soil. Plant assay experiment demonstrates that CAN can significantly restrain the uptake and accumulation of Pb(II) and Cu(II) ions in vegetables, with a high removal efficiency up to 90.7% and 81.4%, respectively. This work demonstrates a "soil for soil-remediation" strategy to utilize the natural loess for soil remediation in CLP, which paves the way for developing green and sustainable remediation eco-materials with local loess as raw materials.

Ions-induced gelation of alginate: Mechanisms and applications

Alginate is an important natural biopolymer and has been widely used in the food, biomedical, and chemical industries. Ca²⁺-induced gelation is one of the most important functional properties of alginate. The gelation mechanism is well-known as egg-box model, which has been intensively studied in the last five decades. Alginate also forms gels with many other monovalent, divalent or trivalent cations, and their gelation can possess different mechanisms from that of Ca²⁺-induced gelation. The resulted gels also exhibit different properties that lead to various applications. This study is proposed to summarize the gelation mechanisms of alginate induced by different cations, mainly including H⁺, Ca²⁺, Ba²⁺, Cu²⁺, Sr²⁺, Zn²⁺, Fe²⁺, Mn²⁺, Al³⁺, and Fe³⁺. The mechanism of H⁺-induced gelation of alginate mainly depends on the protonation of carboxyl groups. Divalent ions-induced gelation of alginate show different selection towards G, M, and GM blocks. Trivalent ions can bind to carboxyl groups of uronates with no selection. The properties and applications of these ionotropic alginate gels are also discussed. The knowledge gained in this study would provide useful information for the practical applications of alginate.