Oil-contaminated soils resulted from drilling activities can cause significant damages to the environment, especially for living organisms. Treatment and management of these soils are the necessity for environmental protection. The present study investigates the field study of seven oil-contaminated soils treated by different stabilization/solidification (S/S) methods, and the selection of the best treated site and treatment method. In this study, first, the ratios of consumed binders to the contaminated soils (w/w) and the treatment times for each unit of treated soils were evaluated. The ratios of consumed binders to the contaminated soils were between 6 and 10% and the treatment times for each unit of treated soils were between 4.1 and 18.5 min/m³. Physicochemical characteristics of treated soils were also determined. Although S/S methods didn’t change the water content of treated soils, they increased the porosity of soils. Unexpectedly, the cement-based S/S methods didn’t increase the pH of the treated soils. The highest and the lowest leaching of petroleum hydrocarbons was belonging to S/S using diatomaceous earth (DE) and the combination of Portland cement, sodium silicate and DE (CS-DE), respectively. The best acid neutralization capacity was obtained for soils treated using the combination of Portland cement and sodium silicate (CS). Based on the best-worst multi-criteria decision-making method (BWM-MCDM), the soils treated using CS-DE was select as the best. The BWM-MCDM can be used as an effective tool for the selection of the best alternative in all areas of environmental decontamination.

Three types of diatomite-based adsorbents—diatomaceous earth (DE), purified diatomite (PD), and diatomite@MgO/CaO (D@MgO) were used for adsorption decontamination of ammonium from Lake Qarun water (28.7 mg/L). The adsorption properties of the three diatomite-based adsorbents were evaluated by both batch and fixed-bed column adsorption studies. The kinetic results demonstrated removal percentages of 97.2%, 69.5%, and 100% using DE, PD, and D@MgO, respectively, at a 1 g/L adsorbent dosage. The adsorption results using DE and D@MgO showed the best fitness with pseudo-first-order kinetic and Langmuir isotherm models, while the obtained results using PD demonstrate better fitness with the Freunlidich model. The recognised fitting results with the pseudo-first-order model and estimated adsorption energies demonstrated physical uptake of ammonium by DE (5.93 kJ/mol), PD (4.05 kJ/mol), and D@MgO (7.81 kJ/mol). The theoretical maximum ammonium uptake capacity of DE, PD, and D@MgO were 63.16 mg/g, 59.5 mg/g, and 78.3 mg/g, respectively. Using synthetic adsorbents in a fixed-bed column system for treating ammonium ions in Lake Qarun water resulted in removal percentages of 57.4%, 53.3%, and 62.6% using a DE bed, PD bed, and D@MgO bed, respectively, after treating approximately 7.2 L of Lake Qarun water using a bed thickness of 3 cm, a flow rate of 5 mL/min, pH 8, and the determined ammonium concentration in Lake Qarun water (28.7 mg/L). The curves demonstrated breakthrough times of 900 min, 900 min, and 960 min for the DE bed, PD bed, and D@MgO bed, respectively, with 1440 min as the saturation time. The columns’ performances also were studied based on the Thomas model, the Adams-Bohart model, and the Yoon-Nelson model.

The N-TiO2/g-C3N4@diatomite (NTCD) composite has been prepared through a simple impregnation method, using titanium tetrachloride as precursor and urea as nitrogen-carbon source. Then the effects of calcination temperature on structure, surface property and photocatalytic activity of the catalysts were investigated. And XRD, TEM, XPS, FTIR and UV–vis diffuse adsorption spectroscopy were used to characterize the obtained powders. The photocatalytic activity of the NTCD was evaluated through the reduction of aqueous Cr (VI) under visible light irradiation (λ > 400 nm). The results demonstrated that the nano-TiO2 particles ranging from 15 to 30 nm in the crystal of anatase are well deposited on the surface of diatomite in the NTCD-500 which calcined at 500 °C for 2 h. Furthermore, the g-C3N4 with the lay thickness of 0.92 nm was attached to the surface of nano-TiO2. The N-doped TiO2 and g-C3N4 doped catalysts could co-enhance response in the visible light region and reduce band gap of NTCD-500 (Eg = 3.07 eV). And the NTCD-500 sample exhibited nearly 100% removal rate within 5 h for photocatalytic reduction of Cr (VI) which was higher activity than P25, crude TiO2@diatomite and g-C3N4@diatomite.

Air pollution control (APC) residues, which are known to be the byproducts of incineration treatment, exhibit a high leaching potential of toxic metals. Calcium silicate hydrate (C-S–H), which is a major hydration product of hardened cement and immobilizes toxic metal, can be formed by the reaction of Ca with pozzolanic Si in a highly alkaline environment. Toxic metals might be immobilized by the addition of pozzolanic material to APC residues (instead of using cement), which is a Ca source and provides an alkaline condition. In this study, diatomite, which mainly comprises amorphous silica (SiO₂·nH₂O), was investigated as a pozzolanic material for Pb immobilization in APC residues obtained from a municipal solid waste incinerator. APC residues were cured with and without the addition of diatomite at different temperatures. When diatomite was added to APC residues, pozzolanic phases such as C-S–H gel were formed via the consumption of Ca(OH)₂ and CaClOH. Compared to APC residues cured without diatomite, the leaching of Pb decreased by 99% for APC residues cured for 14 days with 10% diatomite at 70 °C. The results of sequential chemical extraction showed that water-soluble Pb in APC residues was reduced from 10.3% to nearly zero by the pozzolanic reaction. Consequently, the leaching amount of Pb dropped below 0.3 mg/L (Japanese criteria for landfill disposal). Overall, these experiments provide promising results regarding the possibility of using diatomite for pretreating APC residues.

In this study, cationic polyacrylamide (CPAM)-modified diatomite and cetyl trimethyl ammonium bromide (CTAB)-modified diatomite were synthesized and used as conditioners for sewage sludge dewatering. The effects of these two types of modified diatomite on the dewaterability and settling performance of the activated sludge were studied. The mechanisms of the two modified diatomite types in the activated sludge system were elucidated. The efficiency of the CPAM-modified diatomite was better than that of the CTAB-modified diatomite in improving the settleability and dewaterability of sludge. The results indicated that specific resistance to filtration (SRF) was decreased from 8.52 × 10¹² to 0.92 × 10¹² m/Kg, and the water content in the remaining sludge cake after pumping filtration was decreased from 92.2 to 68.1% by adding 0.4% of CPAM-modified diatomite and pH = 3.5, which resulted in excellent sludge settling of activated sludge. Further studies showed that the polymer/surfactant adsorbed in diatomite increased sludge dewaterability and improved the sedimentation rate owing to stripping extracellular polymeric substances (EPS) and damaging the internal structure of the sludge, leading to sludge conduce bound water release. According to scanning electron microscope (SEM) images, the two types of modified diatomite powder maintained the porous structure and showed a more complete and uniform structure compared to natural diatomite.

In this study, diatomite coated with Fe-Mn oxides (DFMO) was synthesized through calcination. The adsorption of antimonate (Sb(V)) by DFMO was studied, and environmental factors affecting the adsorption were investigated. The components of DFMO were identified as γ-Fe₂O₃, γ-MnO₂, and SiO₂, in the presence of diatomite covered with nanoscale metal oxides. Batch experiments were carried out to evaluate the antimonate adsorption performance in aqueous solution. Results showed that maximum Sb(V) adsorption capacity of DFMO reached 10.7 mg/g at pH 4, corresponding to 22.2 mg/g per unit metal oxides. Antimonate adsorption occurred on heterogenous surface, following the Freundlich and Pseudo-second order model. Overall, antimonate adsorption was favored at acidic condition due to low point of zero charge. However, when treating electroplating wastewater, neutral pH condition exhibited a higher efficiency than acidic pH, because co-existing ions in electroplating wastewater significantly affects antimony adsorption. Further investigation showed that among different potential co-existing ions, fluoride can strongly inhibit the adsorption of antimonate at 5 mg/L under pH 4. Density functional theory (DFT) analysis confirmed that adsorption energy on DFMO follows: HF < F⁻ < Sb(OH)₆⁻, indicating that fluoride is easier to bind with DFMO compared to antimonate, especially under pH 3.5 at which fluoride exists as HF. Moreover, the competitive adsorption of fluoride toward antimonate indicated the necessity of pre-treatment like neutralization and precipitation before adsorption process.

Diatomite (D) as a low-cost and eco-friendly clay was modified by ethylene diamine (EDA)-trimesoyl chloride (TMC) polymer to achieve a novel adsorbent for efficient removal of rhodamine B dye (RB) from wastewater samples. The EDA-TMC polymer was grafted to the surface of diatomite by in situ interfacial polymerization. The prepared p(EDA-TMC)/D adsorbent was characterized by XRD, FTIR, and SEM/EDX techniques. The effective experimental parameters on the adsorption performance were optimized with factorial design analysis. The equilibrium data were better correlated by non-linear Langmuir model compared to non-linear Freundlich model. The Langmuir monolayer adsorption capacity of the p(EDA-TMC)/D adsorbent was determined as 371.8 mg g⁻¹. The key adsorption parameters were optimized by experimental design analysis. The kinetic findings showed the adsorption mechanism of RB onto p(EDA-TMC)/D adsorbent was well designated by the pseudo-second-order kinetic model. The thermodynamic results indicate that the RB adsorption had an exothermic character in thermal nature and was less favorable with increasing temperature from 20 to 60 °C. Furthermore, the adsorption/desorption yield of p(EDA-TMC)/D was still 80%/70% after 5ᵗʰ cycle and reduced to 60%/52% at the end of 8ᵗʰ cycle. Thus, the present study revealed that the developed p(EDA-TMC)/D composite had great adsorption potential for removal of RB from wastewater samples compared to that of different kinds of adsorbents reported in the literature.

This research analyzes the behavior of different diatomite from Peru, and their potential use for the removal of heavy metals from contaminated effluents. Seven different diatomites were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscopy, specific surface area, and cation exchange capacity. The absolute removal and the removal efficiency of Cu, Pb, and Zn were assessed by stirring the diatomite in solutions of known concentration of the contaminant, and then analyzing the solutions by atomic absorption spectroscopy (AA). The results were finally correlated with microstructural, chemical, and physicochemical characteristics of the diatomites. It was found that Peruvian diatomites have potential use for decontamination of heavy metals from contaminated effluents even with their low SiO₂ content. Affinity for the studied metals was as follows: Zn > Pb > Cu, with removal percentages as higher than 98% for Zn. No one-to-one relationships were found between the removal efficiency of the studied metals with properties of diatomites. Different parameters must be taken into account at the same time to understand the efficiency of metal removal in polluted waters. In this case, the specific surface area and minor oxides have the greatest effect on the removal efficiency of all metals.

A waste–struvite/diatomite compound (MAP@Dia) recovered from nutrient-rich wastewater treated by MgO-modified diatomite (MgO@Dia) was provided to immobilize lead in aqueous solution and contaminated soil. The mechanism and effectiveness of lead immobilization was investigated, and the pHₛₜₐₜ leaching test and fixed-bed column experiments were carried out to assess the risk of MAP@Dia reuse for lead immobilization. The results showed that MAP@Dia were effective in immobilizing lead in aqueous solution with adsorption capacity of 832.47–946.50 mg/g. The main mechanism of Pb immobilization by MAP@Dia could be contributed by surface complexation and dissolution of struvite followed by precipitation of hydroxypyromorphite Pb₁₀(PO₄)₆(OH)₂. Lead(II) concentration reduced from 269.61 to 78.26 mg/kg, and residual lead(II) increased to 53.14% in contaminated soil when the MAP@Dia application rate was 5%. The increased neutralization capacity (ANC) and lower lead extraction yields in pHₛₜₐₜ leaching test in amended soil suggested 5 times of buffering capacity against potential acidic stresses and delayed triggering of “chemical time bombs.” The results of column studies demonstrated that amendment with MAP@Dia could reduce the risk of lead and phosphorus (P) leaching. This study revealed that MAP@Dia could provide an effective solution for both P recycling and lead immobilization in contaminated soil.

This study proposes an improved activation for hydrogen peroxide and persulfate using Fe-modified diatomite (MD) to favorably lead the reaction to generate hydroxyl and sulfate radicals to degrade the contaminants phenanthrene and anthracene. Diatomite was modified by impregnating it with a mixture of ferrous (Fe²⁺) and ferric (Fe³⁺) ions in the form of precipitated iron oxides and hydroxides. The raw and synthesized materials were characterized by powder X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size by laser diffraction, chemical microanalysis of the elements by energy-dispersive X-ray, and scanning electron microscopy (SEM). Batch experiments were performed to compare the new activator material (modified diatomite) with traditional methods of activation for these oxidants and to statistically study the optimum ratio between the amount of this material and the concentration of one oxidant to the degradation of the contaminants phenanthrene and anthracene. The characterization results showed that the materials are amorphous and that the Fe ion concentration was 4.78 and 17.65 % for the raw and modified diatomites, respectively. This result shows a significant increase in the amount of iron ions after synthesis. Comparing the traditional activation method with the modified diatomite, the results of batch experiments showed that the synthesized material presents significant catalytic activity for the oxidation of these contaminants, using sodium persulfate and hydrogen peroxide as oxidants. The analysis of the variables results showed that the concentration of the oxidant has higher significance than the amount of the catalyst.