The production rate of industrial and agricultural waste is increasing due to population growth. Soil is the most important receiver of industrial and agricultural waste. Contaminants such as heavy metals in various waste after reception by the soil, immediately become part of the cycle that has different impacts on the environment. Geopolymer, as a chemical stabilizer has the potential to stabilize heavy metals in the soil. In this research, several geopolymers for the stabilization of heavy metals in soil were synthesized. Silicon dioxide (SiO2) and aluminosilicate (Al2SiO4) must be used to produce the geopolymers. Rice husk ash was used as the SiO2 source. Also, Iranian zeolite and sepiolite, and red clay soil were utilized as the source of Al2SiO4. The synthesized geopolymers were investigated for the adsorption of nickel and cadmium. Also, batch and column studies of using geopolymers for the chemical stabilization of heavy metals in soil were conducted. The results revealed a high adsorption capacity of the geopolymers. The zeolite, sepiolite, and red clay geopolymer-soil samples adsorbed 100% of the heavy metals (i.e., Ni and Cd) at a concentration of 100 ppm. The zeolite geopolymer adsorbent adsorbed 57% and 96% of Ni and Cd at a concentration of 1000 ppm, respectively. In general, it was concluded that the use of geopolymer compounds in soils with high heavy metal adsorption capacity could be an efficient approach to prevent groundwater resource pollution.

Present study reports the laboratory and field scale application of different organic and inorganic amendments to immobilize cadmium (Cd) and lead (Pb) in a co-contaminated alluvial paddy soil. For that purpose, lime, biochar, Fe-biochar and two composite amendments (CA) composed of biochar, lime, sepiolite and zeolite (CA1: composite amendment 1) and manure, lime and sepiolite (CA2: composite amendment 2) were firstly tested in an incubation experiment to ameliorate Cd and Pb co-contaminated alluvial soil. It was observed that liming and CA2 elevated the soil pH and reduced DTPA extractable Cd and Pb in the incubated soil leading to higher metal immobilization. Therefore, efficiency of lime and CA2 was further investigated in field conditions with mid rice as the test crop to evaluate field scale immobilization and precise application rate for the tested soil type. DTPA and CaCl₂ extractable Cd (46 and 51%) and Pb (68 and 70%) in field soil were decreased with applied treatments. Speciation of Cd and Pb also promoted conversion of metal exchangeable contents to less-available forms. Activated functional groups on amendments’ surface (_OH bonding, C_O and CO, -O-H, Si–O–Si, carboxylic and ester groups) sequestered metals by precipitation, adsorption, ion exchange or electro static attributes. Application of lime at 2400 kg/acre (T4) and CA2 at 1200 kg/acre was more effective in reducing rice shoot and grains metal contents. Moreover, obtained results in terms of pH, extractable content, speciation and yield, and microanalysis of amendments highlights the remarkable efficiency of lime and composite amendment to sorb Cd and Pb providing the key evidence of these amendments for metals immobilization and environmental remediation. Considering these results, lime and CA2 are potential amendments for co-contaminated rice field especially in context of alluvial soil.

Long-term effectiveness and persistence are two important criterias to evaluate alternative remediation technology of heavy metal polluted soils. Pot and field studies showed addition of sepiolite was effective in immobilizing Cd in polluted soils, with significant reduction in TCLP extracts (0.6%–49.6% and 4.0%–32.5% reduction in pot and field experiments, respectively) and plant uptake (14.4%–84.1% and 22.8%–61.4% declines in pot and field studies, correspondingly). However, the applications of sepiolite offered a limited guarantee for the safety of edible vegetables in Cd-polluted soils, depending on the soil type, the Cd pollution type and level, and the dose and application frequency of chemical amendments. Bioassays, such as plant growth, soil enzymatic activities and microbial community diversity, indicated a certain degree of recovery of soil metabolic function. Therefore, sepiolite-assisted in situ remediation is cost-effective, environmentally friendly, and technically applicable, and can be successfully used to reduce Cd enter into the food chain on field scale.

Organic and inorganic mixtures can be developed as immobilizing agents that could reduce heavy metal accumulation in crops and contribute to food safety. Here, inorganic materials (lime, L; zeolite, Z; and sepiolite, S) and organic materials (biochar, B, and compost, C) were selectively mixed to produce six composite soil amendments (LZBC, LSBC, LZC, LZB, LSC, and LSB). Given the fact that LZBC showed the best performance in decreasing soil Cd availability in the incubation experiment, it was further applied in the field condition with 14 vegetables as the test crops to investigate its effects on crop safety production in polluted greenhouse. The results showed that LZBC addition elevated rhizosphere soil pH by 0.1–2.0 units and reduced soil Cd availability by 1.85–37.99%. Both the biomass and the yields of edible parts of all vegetables were improved by LZBC addition. However, LZBC addition differently affected Cd accumulation in edible parts of the experimental vegetables, with the observation that Cd contents were significantly reduced in Allium fistulosum L., Amaranthus tricolor L., and Coriandrum sativum Linn., but increased in the three species of Lactuca sativa. Further health risk assessment showed that LZBC application significantly decreased daily intake of metal (DIM), health risk index (HRI), and target hazard quotient (THQ) for Cd in Allium fistulosum L., Amaranthus tricolor L., and Coriandrum sativum Linn., whereas increased all the indexes in Lactuca sativa. Our results showed that the effect of a composite amendment on Cd accumulation in different vegetables could be divergent and species-dependent, which suggested that it is essential to conduct a pre-experiment to verify applicable species for a specific soil amendment designed for heavy metal immobilization.

With the improvement of environmental protection and standards, the recovery and recycling of copper ions released from industrial wastewater discharge has aroused sufficient research interest. A new adsorbent (ABsep) derived from natural sepiolite (Sep) by modification technology of hexadecyltrimethoxysilane (HDTMS) or tetraethylorthosilicate (TEOS) and flocs separation method for adsorption of Cu²⁺ in wastewater have been investigated in this paper. The changes of crystal structure and physicochemical properties of Sep during modification process showed that HDTMS and TEOS were loaded onto the Sep surface without inserting into the Sep interlayer structure. The adsorption experimental results presented a smaller amount of ABsep (1 g/L) achieved 97.5% removal of 50 mg/L Cu²⁺ at pH 6 and temperature of 298 K within a shorter contact time (50 min). It is interesting the adsorption process of Cu²⁺ on ABsep was spontaneous and exothermic, with physical adsorption dominating, as result of combination of physical adsorption, electrostatic gravitational force, and chemical reaction. Because of good physical–chemical adsorption performance of ABsep surface to Cu²⁺, high removal rates of Cu²⁺ from aqueous phase could be achieved after three adsorption regeneration cycles, this indicated the ABsep was expected to be a promising adsorbent of Cu²⁺ removal for wastewater treatment.

Various geochemical studies have yielded conflicting data on whether humic coatings decrease or increase adsorption of heavy metals by soil minerals. The objective of the present study is to determine how humate pre-adsorption affects subsequent retention of Cd and Pb by palygorskite and sepiolite, as special silicate clay minerals of soil in many arid regions. For this purpose, a series of equilibrium batch experiments were conducted on the interactions of Pb and Cd with Ca–palygorskite and Ca–sepiolite before and after humate adsorption. The results showed that the Langmuir (L), Freundlich (F), Langmuir–Freundlich (LF), and Toth (T) equations satisfactorily described metal sorption data on the minerals. In the presence of humate as the pre-adsorbate, the values for sorption capacities of palygorskite and sepiolite for Cd and Pb slightly decreased. This can be attributed to the competition between humates and metal ions for mineral active sites and steric hindrance of the adsorbed humates, which reduces the access of metal ions to the mineral surface and internal channels. Humate coatings decreased the adsorption equilibrium constants of Cd, suggesting that the affinity of the organo-clays for Cd sorption is lower than those of Ca–clays. The values for the heterogeneity factor (β) generally showed an increasing trend with increasing humate coverage on palygorskite and sepiolite, which can be explained by the increased diversity of adsorption centers on humate–clay complexes. It may be concluded that the presence of humate bound on fibrous clay surfaces can influence the sorption, and hence the bioavailability and mobility of heavy metals in fibrous clay-containing arid and semiarid soils.

Waste management is the protection of the environment and the health of the population. Paper waste sludge is produced during paper production and sepiolite is a natural clay mineral. The aim of the study was to investigate the usability of sepiolite-added paper waste sludge as a bedding material in the broiler production. Two hundred eighty-eight 1-day old male broiler chicks were divided into the 6 bedding material groups (wood shavings (control), paper waste sludge, sepiolite, mix of 25% paper waste sludge and 75% sepiolite, mix of 50% paper waste sludge and 50% sepiolite, and mix of 75% paper waste sludge and 25% sepiolite) with 6 replicate pens per group. Litter quality, performance, and some welfare parameters of broilers were assessed during the 6 weeks’ period. Body weight at 42 days of age and body weight gain from 0 to 42 days of broilers reared on the wood shavings and mix of 50% paper waste sludge and 50% sepiolite were found higher than those of the sepiolite and paper waste sludge groups. Feed consumption and feed to gain ratio from 0 to 42 days, yields of carcass and carcass parts, percentages of organs and abdominal fat, IgG, percentage of bursa Fabricius, burns of foot pad and breast, litter pH and meat properties of broilers reared on the wood shavings, paper waste sludge, and sepiolite litter groups were not found to be statistically different. Litter moisture was found higher in the paper waste sludge group than that in the sepiolite group at the 42 days of rearing. As a conclusion, usage of mix of 50% paper waste sludge and 50% sepiolite as a litter does not have any negative effects on performance, welfare, and litter quality. This result is important in terms of utilizing a waste product.

The effects of low molecular weight organic acids (LMWOAs) on the adsorption of quinclorac by sepiolite were investigated using laboratory batch technique. Experiments were conducted with two natural sepiolite samples with different crystal structures and chemical compositions and high-purity sepiolite. The LMWOAs used were acetic, oxalic, and citric acid. And the adsorption mechanism was characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Our analysis revealed that adsorption of quinclorac on α-sepiolite and β-sepiolite was inhibited in the presence of 4 mmol L⁻¹ LMWOAs, whereas LMWOAs stimulated the adsorption of quinclorac in the high-purity sepiolite. Inhibition or stimulation varied across the different types of organic acids. The adsorption isotherms in the presence of 4 mmol L⁻¹ LMWOAs were better explained by Freundlich and linear model. The effect of organic acid concentrations (0–32 mmol L⁻¹) on the adsorption of quinclorac by the three sepiolite samples varies greatly depending on the type of organic acid and the property of sepiolite. FTIR, XRD, and XPS analyses showed that LMWOAs bound strongly to the Si–O bond structure, and Si–O-quinclorac-acetic acid (oxalic acid or citric acid) was formed on the surface of β-sepiolite. The adsorption of quinclorac by β-sepiolite was via hydrogen bond, complexation reactions, and charge transfer in the presence of LMWOAs. These results indicate that LMWOAs affect quinclorac adsorption through various interactions involving competition, electrostatic attraction, bridging action, and hydrogen bonding.

Sepiolite reveals as a low-cost and efficient adsorbent for the adsorption of caffeine from aqueous solutions. The characterization of this material was carried out by N₂ adsorption–desorption at 77 K, Fourier transform infrared spectroscopy, thermogravimetric analysis, and electronic microscopy. Initially, batch adsorption experiments were developed in order to determine the equilibrium time and the adsorption isotherm of the system. Pseudo–first-order, Elovich equation, pseudo–second-order, and intra-particle diffusion models were applied to the experimental data to determine the adsorption kinetics. In continuous adsorption, the influence of several operation conditions (initial caffeine concentration, volumetric flow rate, and mass of adsorbent) on the shape of breakthrough curves and the mass transfer resistance was evaluated. Experimental data were fitted to the bed-depth service-time model bed-depth service-time (BDST). Through the calculation of the adsorption, parameters as breakthrough time or caffeine removal percentage can be concluded that the removal of this compound from aqueous solutions by adsorption in sepiolite beds is an alternative technique to the current methods, in order to eliminate this micropollutant.

Farmland soils that surround a historical zinc smelting area in northwestern Guizhou, China, are characterized by high levels of heavy metal accumulation. Previous studies have mainly focused on the potential risk evaluations of heavy metals in soil and crops. However, at present, the effects of amendment applications on the bioavailability of heavy metals and on microbial community in the heavily contaminated soils of the mining region are still unclear. A pot experiment was conducted to determine the effect of applying a combined amendment (e.g. lime, sepiolite, and vermicompost) on the diversity and composition of microbial community in the contaminated soil. The results showed that the contents of DTPA- and TCLP-extractable heavy metals (e.g. Cd, Pb, and Zn) decreased and that the pH, SWC, EC, and soil available nutrient (e.g. AN, AP, and AK) contents increased after the application of the combined amendment. Furthermore, application of the combined amendment decreased the diversity of soil bacterial and fungal communities and increased the relative abundances of the dominant bacterial and fungal communities such as Proteobacteria, Bacteroidetes, and Ascomycota; however, the relative abundances of Acidobacteria and Actinobacteria decreased. Redundancy analysis (RDA) and structural equation model (SEM) analysis showed that the bioavailability of heavy metals decreased and that soil physicochemical characteristics improved and had positive or negative effects on the diversity and composition of soil microbial community.