The sorption behaviors of brilliant blue FCF dye by natural clay and modified with iron chloride were determined. The materials were characterized by X-ray diffraction and scanning electron microscopy, and the zero point charges were also determined. The effects of pH, contact time, dye concentration, and temperature were considered. The results showed that clay does not suffer any important change in its structure after the chemical treatments. The pH influences the sorption of the dye in the unmodified clay, but this effect was not observed in the iron-modified clay. The equilibrium time and the sorption capacity for the unmodified clay were 48 h and 6.16 mg/g, while for the iron-modified clay, 24 h and 14.22 mg/g, respectively. The sorption kinetics results were best adjusted to the pseudo-first-order and pseudo-second-order models. Sorption isotherms were best adjusted to the Langmuir model, indicating that both clays have a homogeneous surface. Thermodynamic parameters (E, ΔS, ΔG and ΔH) were calculated for the natural clay from the data of the sorption kinetics at temperatures between 20 and 50 °C, indicating that the sorption process is exothermic. For the case of the iron-modified clay, it was not possible to calculate these thermodynamic parameters because the sorption capacities were similar in the temperature range selected.

Organoclays possess unique adsorption behaviour towards hydrophobic organic contaminants. They can also remediate ionic contaminants such as heavy metals and metalloids. The objective of the present study was to prepare organoclay and organoclay mixtures efficient to adsorb both cationic and anionic contaminants. The adsorbents were characterised by X-ray diffraction and infrared spectroscopy. Trivalent (Cr3+) and hexavalent (Cr2O 7 2-) chromium were selected as the model contaminants representing cationic and anionic properties. Bentonite modified with cationic surfactant hexadecyl trimethylammonium bromide at double the cation exchange capacity of the clay remarkably improved Cr2O7 2- adsorption capacity (as high as 0.49 mmol g-1). Similarly, its modification with anionic surfactant sodium dodecyl sulphate at the same dosage improved Cr3+ adsorption (as high as 0.36 mmol g -1). When these two organoclays were physically mixed in equal proportions (1:1), the resultant organoclay mixture efficiently adsorbed both Cr3+ (as high as 0.21 mmol g-1) and Cr2O 7 2- (as high as 0.32 mmol g-1) implying that the mixture could remediate both anionic and cationic contaminants simultaneously. The adsorption of Cr3+ by the organoclay and organoclay mixture fitted well to the Langmuir isothermal model whereas the adsorption of Cr2O7 2- fitted well to the Freundlich model. © 2013 Springer Science+Business Media Dordrecht.

Acid mine drainage (AMD) has long been a significant environmental problem that impairs water resources in historic or current mining industries throughout the world. One of the methods using passive treatment system at low cost to remove metals from solution involves the use of clays. The ability of three different adsorbents (montmorillonite K-10, bentonite (NT-25), and hydrotalcite (HT)) to remove Fe and Mn from aqueous solutions and acid mine drainage samples has been studied at different optimized conditions such as pH, amount of adsorbent and contact time. Flame atomic absorption spectrometer (FAAS) was used for measuring Fe and Mn concentrations. Langmuir and Freundlich isotherms were applied and isotherm coefficients were computed. A kinectic study was also developed for HT using the first order, second order and intraparticle diffusion models. A great amount of clay (more than 100 mg) and also contact times higher than 60 min had also no influence in the adsorption capacity for all adsorbents. HT was found to be the best among the studied clays removing more than 90 % of Fe and Mn for all AMD samples investigated. Moreover, the maximum adsorption capacity was 63.7 mg Mn g⁻¹ HT and 666.7 mg Fe g⁻¹ HT.

In this article, dynamic simulation experiments have studied the effects of three capping materials, quartz sand (QS), aluminum-based phosphorus-locking agent (Al-PIA), and lanthanum-modified bentonite (LMB) in reducing phosphorus load in eutrophic water bodies. The changes of various forms of phosphorus in Al-PIA and sediment before and after the test were analyzed, and the mechanism of phosphorus migration and transformation in different capping systems was described. The dynamic simulation test lasted 95 days. The results showed that when the initial concentration of total phosphorus (TP) was 3.55 mg/L, the capping strength was 2 kg/m² and the hydraulic retention time of water circulation was 0.5 days, indicating that the average reduction rates of TP by LMB, Al-PIA and QS systems were 74.66%, 69.54%, and 3.64%, respectively, compared with the control system. The analysis of variance showed that there were significant differences (P < 0.05) in the TP concentration of the overlying water between the LMB, Al-PIA capping system, and the control system. Lanthanum ions in LMB can fix phosphorus. Al-PIA reduces the phosphorus concentration in water by means of ion exchange, adsorption, complexation, etc. LMB and Al-PIA promoted the migration of phosphorus in sediment. Among them, the phosphorus fixed by Al-PIA was mainly in the form of non-apatite inorganic phosphorus (NAIP) in inorganic phosphorus (IP), which can be seen; Al-PIA can effectively reduce the phosphorus load of eutrophic water.

Worldwide, freshwater environments are impacted by inputs of nutrients and dissolved organic matter from human activities. Yet, the recovery of aquatic systems is usually focused only on nutrient management. In our work, we presented the case of an urban and hypereutrophic environment (Pampulha reservoir, Belo Horizonte, Brazil) that receives discharges from several streams and was treated with lanthanum modified bentonite (Phoslock®) and microbial bioremediation (Enzilimp®). Our goals were to evaluate whether the treatment could improve the water quality and characterize the spatiotemporal variation of dissolved organic matter sources and indices according to absorbance and fluorescence measurements from the reservoir and streams post-application months (2018). In our results, the reservoir showed a relative decrease in its phosphorus concentration compared to data from before the treatment. On the other hand, carbon concentrations reached expressive values in the post-application months following a similar pattern found in the streams. Our data showed that the reservoir’s high resistance in its hypereutrophic condition was related to the elevated loading of external inputs coming from the streams. The parallel factor analysis (PARAFAC) identified four main carbon sources, two of them being potential tracers of organic pollution in the Pampulha reservoir and watershed, together with absorbance and fluorescence indices. Our findings suggest that carbon parameters can be essential tools to provide adequate monitoring and optimization of water recovery attempts in complex, polluted environments.

In this study, an innovative material (nitrogen, phosphorus, and oxygen controlling agent, NOC) was synthesized by calcium peroxide (CaO₂), magnesium chloride (MgCl₂), bentonite, zeolite, cement, stearic acid (SA), citric acid (CA), and silver sand. The treatment performance of NOC in mimic black-odor river water was investigated in lab-scale, and the results showed that over 73.7% phosphorus and 77% ammonia nitrogen were removed from river water with the addition of 470 g NOC at 30 mL h⁻¹ flow rate, demonstrating that the presence of NOC could remove phosphorus and ammonia nitrogen simultaneously. Moreover, the addition of NOC could release oxygen with tender influence on pH in water. Calcium phosphate (Ca-P), aluminum phosphate (Al-P), and ferric phosphate (Fe–P) in the river sediment increased from 1.6, 0.136, and 0.12 mg g⁻¹ to 2.16, 0.242, and 0.196 mg g⁻¹ for 28 days, respectively. The results manifested that the mobile phosphorus could be adsorbed by NOC and further transformed to inert phosphorus form, thereby restraining the release of endogenous phosphorus from sediment to the overlying water. Besides, the relative abundance of microorganisms could be enhanced with the existence of NOC, further promoting the removal of phosphorus. Hence, NOC could be applied to the efficient remediation of the black-odor river.

The attempt of the current study is to find an eco-friendly method for managing the solid waste deposited in the landfill of used motor oil recovery factories through the fabrication of zeolite-based compounds. This toxic waste is originated from the application of natural bentonite, traditionally used as an effective adsorbent in the recovery process. The black waste was converted to zeolite structures through the fusion technique. Firstly, the collected powder was mixed with sodium hydroxide, and boehmite followed by the thermal treatment at different temperatures, 600–800 °C. Then, the obtained precursors were hydrothermally converted to zeolite A or hydroxysodalite. The effects of processing factors like alkalinity, boehmite, and sodium aluminate ratios (respect to solid waste mass), fusion temperature, and aging time on the structural characteristics, and cation exchange capacity (CEC) were studied in detail. In order to achieve a cation exchange capacity of about 190 mg g⁻¹, the alkali and boehmite ratios should be adjusted at 2.00 and 0.53, respectively. Based on the morphological observations, the fusion at 800 °C caused the formation of cubic particles with sharp edges. Besides, the hydrosodalite powder with the extended surface area, 77 m² g⁻¹, could be produced by fixing the boehmite, and sodium aluminate ratios at the levels of 0.13 and 0.40, respectively.

The demand for rare earth elements (REEs) is likely to outweigh supply. As such, every effort should be taken to salvage REEs from waste streams and other sources of discharge. In this study, PHREEQC geochemical modelling code coupled to parameter estimation software (PEST) was used to simulate the adsorption of REEs onto generalised sorption sites representing natural bentonite. Experimental observations and bentonite characterisation were used to calibrate the model. A total of 83–99.9%, 57–99.5%, 29–99% and 1–85% adsorption efficiencies were observed at 2, 5, 10 and 50 mg L⁻¹ initial concentration, respectively. The adsorption efficiency (> 99%) of REEs at pH 6 was not affected by the presence of anions and cations at different concentrations. Thus, PHREEQC modelling coupled to PEST can be used to simulate the adsorption of elements using limited data. This study indicated that natural bentonite is a suitable and competent adsorbent for the recovery of REEs from wastewater.

When oil is released into the oceans, spilled oil may get to the shoreline driven by wind and wave. This study comprehensively explored the effects of bentonite nanoclay on the oil behaviors in a water–sand system from both experimental and modeling perspectives. Four factors including nanoclay concentration, temperature, salinity, and pH have been studied. The increasing nanoclay concentration resulted in the decrease in remaining oil on sand. Higher temperature and salinity were associated with less residual oil on sand in the presence of nanoclay. The lower residual oil on sand with coexisting nanoclay was found to be at pH 7. The factorial analysis results indicated that the nanoclay concentration showed the most significant impact among these factors. Miscibility modeling results showed an increasing temperature was favorable to the nanoclay miscibility. Moreover, the effect of nanoclay on oil behavior was further revealed through the dynamic simulation, in which it can be seen the nanoclay could penetrate into oil droplets and promote the oil detachment from solid substrate. The results of this study can help understand the role of fine particles in the fate and transport of oil on shoreline and support the risk assessment and response planning after oil spill.

High concentrations of heavy metals in groundwater are harmful to humans and ecological receptors. This study uses natural alginate-based sorbents for the removal of heavy metals (e.g., copper, zinc, iron, and nickel) from water. The effectiveness of alginate-based sorbents was enhanced by adding calcium bentonite clay and by tuning the porosity of the sorbents. Controlled porosity was obtained by an acid base reaction, using sodium carbonate and acetic acid. The maximum sorption capacity of alginate-based sorbents was 127.9 ± 0.6 mg/g and 148.1 ± 0.2 mg/g for Cu(II) and Zn(II), respectively. The sorption of Zn(II) onto the sorbents followed pseudo first-order kinetics (k₁ = 9.71 × 10⁻³), indicating that the rate limiting step was the diffusion of Zn(II) into the sorbents. In contrast, the sorption of Cu(II) onto the sorbents followed pseudo second-order kinetics (k₂ = 5.80 × 10⁻⁵), indicating that the rate limiting step was chemisorption of Cu(II) into the sorbents. Optical microscopy images of the sorbent cross-section showed pore shrinking following sorption of either Zn(II) or Cu(II), due to crosslinking of alginate by these metal ions. Cu(II) diffusion into the sorbents was further demonstrated by blue discoloration (as shown by images of their cross sections) and by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Intraparticle diffusion plots of both Zn(II) and Cu(II) showed that the sorption process begins with surface adsorption and is followed by the rate controlled step of intraparticle diffusion. Alginate-based sorbents could also be used to effectively remove other divalent ions (e.g., Ni(II)), whereas removal of trivalent ions (e.g., Fe(III)) was less effective.