Removal of antimony from model solutions, mine effluent, and textile industry wastewater with Mg-rich mineral adsorbents

Naturally occurring layered double hydroxide mineral, brucite (BRU), was compared with hydromagnesite (HYD) and a commercial Mg-rich mineral adsorbent (trade name AQM PalPower M10) to remove antimony (Sb) from synthetic and real wastewaters. The BRU and HYD samples were calcined prior to the experiments. The adsorbents were characterized using X-ray diffraction, X-ray fluorescence, and Fourier transform infrared spectroscopy. Batch adsorption experiments were performed to evaluate the effect of initial pH, Sb concentration, adsorbent dosage, and contact time on Sb removal from synthetic wastewater, mine effluent, and textile industry wastewater. Several isotherm models were applied to describe the experimental results. The Sips model provided the best correlation for the BRU and M10. As for the HYD, three models (Langmuir, Sips, and Redlich-Peterson) fit well to the experimental results. The results showed that the adsorption process in all cases followed the pseudo-second-order kinetics. Overall, the most efficient adsorbent was the BRU, which demonstrated slightly higher experimental maximum adsorption capacity (27.6 mg g-1) than the HYD (27.0 mg g-1) or M10 (21.3 mg g-1) in the batch experiments. Furthermore, the BRU demonstrated also an efficient performance in the continuous removal of Sb from mine effluent in the column mode. Regeneration of adsorbents was found to be more effective under acidic conditions than under alkaline conditions.

Chrysotile asbestos treated with phosphoric acid as an adsorbent for ammonia nitrogen

The purpose of this study was to find an alternative application for chrysotile asbestos, given that there is a complete structure of extraction and production of this class of serpentine minerals, but its use is banned for many applications. The idea was to obtain a compound that could immobilize phosphate by triggering a reaction between the magnesium oxide and hydroxide contained in the mineral, without causing phosphate leaching. To this end, chrysotile (Mg₃SiO₅(OH)₄) was treated with phosphoric acid (H₃PO₄) in a molar ratio of 1:3 in an aqueous medium at 85 °C until the solvent evaporated, resulting in two different solid compounds, which were prepared in a similar manner. The first compound (cri/H₃PO₄ 1:3)₁, was obtained by rinsing and then heat-treating it at 150 °C for 6 h, while the second one, (cri/H₃PO₄ 1:3)₂, was rinsed after the heat treatment. Compound (cri/H₃PO₄ 1:3)₁ underwent partial leaching, while compound (cri/H₃PO₄ 1:3)₂ showed a mass increase of 48%, with the formation of crystalline magnesium pyrophosphate mixed with amorphous SiO₂. The latter compound adsorbed N–NH₃ at pH 10, following the pseudo-first-order model (activation energy = 8329 ± 1696 J mol⁻¹). Equilibrium experiments, which were performed following Hill's sigmoidal type S2 isotherm model, indicated that the adsorption phenomenon was governed by two processes, i.e., complexation up to the inflection point (K_H between 10.0 mg L⁻¹ at 40 °C and 13.6 mg L⁻¹ at 25 °C) followed by adsorption. The q_max varied from 18.0 to 19.6 mgN g⁻¹ and the adsorbent was reusable, maintaining its initial adsorbent capacity during its first reuse. This material, which was tested on real effluents, presented a N–NH₃ removal rate similar to that shown by the test solutions. The treatment of chrysotile with H₃PO₄ conducts it to a composite that adsorbs ammoniacal nitrogen at pH 10 and it is reusable maintaining the adsorption capacity.

Superior removal of selenite by periclase during transformation to brucite under high-pH conditions

The sorption of selenite (Se(IV)) at trace (sub-ppm) to high concentrations on periclase (MgO) under high-pH conditions (pH > 10) was examined by macroscopic sorption experiments and nanoscale solid phase analyses via transmission electron microscopy and X-ray absorption spectroscopy. The maximum distribution coefficient (K_d) of Se(IV) on MgO was 100 L/g, the highest among any reported mineral sorbents at pH > 10. Since MgO is a metastable phase under ambient conditions, it transforms instantaneously to brucite (Mg(OH)₂) in solution. Se(IV) was preferentially and homogeneously distributed onto the newly formed Mg(OH)₂. The Mg(OH)₂ formed thin flake-like platelets, which appeared to be aggregates of nanoscale Mg(OH)₂ particles, the primary alteration product of MgO. The chemical form of Se(VI) adsorbed on nanoscale particles was outer-sphere complexes. Therefore, the outer-spherically adsorbed Se(IV) was occluded into the large flake-like Mg(OH)₂ particles, resulting in its effective isolation from the solution.

Synthesis of Mg-Al layered double hydroxides by electrocoagulation

Recently, layered double hydroxides (LDHs) have attracted much consideration due to their versatility and easily manipulating properties and their potential applications such as anion exchangers, support of catalysts, flame retardants, biomedical drug delivery. A novel method for the in-situ preparation in situ of LDHs, using electrocoagulation (EC) processes was developed, the EC process was performed under two different conditions, at 5 mA m⁻², changing polarity of the electrodes to find out the composition that leads to LDHs generation. The final product was characterized using XRD, BET and FTIR techniques.

This method presented the following advantages: (1) Simultaneously LDHs synthesis and wastewater treatment by ion removal; (2) Polarity control allows to manipulate the M²⁺/M³⁺ molar ratio, LDHs properties and its potential applications; (3) The method spent less time to carry out the synthesis and; (4) it did not need complicated solid-liquid separation processes.

The interface interaction behavior between E. coli and two kinds of fibrous minerals

In the present, studies of interaction between human normal flora and fibrous mineral are still lacking. Batch experiments were performed to deal with the interaction of Escherichia coli and two fibrous minerals (brucite and palygorskite), and the interface and liquid phase characteristics in the short-term interaction processes were discussed. The bacterial concentrations, the remnant glucose (GLU), pyruvic acid, and the activity of β-galactosidase and six elements were measured, and the results show that the promoting effect of brucite on the growth of E. coli was more significant than that of palygorskite. FTIR and XRD analysis results also confirmed E. coli has obviously dissolved on brucite and damage effect on palygorskite silicon structure. SEM results show that the interfacial contact degree between E. coli cells and brucite fibers was higher than that of palygorskite. These may be due to the zeta potential difference between E. coli and palygorskite was 14.57-22.37 mV, while it of brucite was 44.04-64.24 mV. The elements dissolving of two fibrous minerals not only increased regularly to liquid EC but also had a good buffer effect to the decrease of liquid pH. Studies of short-term interaction between E. coli and brucite and palygorskite can help to understand the effect of fibrous minerals on microeubiosis of human normal flora and the contribution of microbial behaviors on the fibrous minerals weathering in the natural environment.

Binding of Nucleic Acid Components to the Serpentinite-Hosted Hydrothermal Mineral Brucite

The adsorption of nucleic acid components onto the serpentinite-hosted hydrothermal mineral brucite has been investigated experimentally by determining the equilibrium adsorption isotherms in aqueous solution. Thermodynamic characterization of the adsorption data has been performed using the extended triple-layer model (ETLM) to establish a model for the stoichiometry and equilibrium constants of surface complexes. Infrared characterization of the molecule-mineral complexes has helped gain insight into the molecular functional groups directly interacting with the mineral surface. Quantum mechanical calculations have been carried out to identify the possible complexes formed on surfaces by nucleic acid components and their binding configurations on mineral surfaces, both in the presence of water molecules and in water-free conditions. The results indicate that brucite favors adsorption of nucleotides with respect to nucleosides and nucleobases from dilute aqueous environments. The surface of this mineral is able to induce well-defined orientations of the molecules through specific molecule-mineral interactions. This result suggests plausible roles of the mineral brucite in assisting prebiotic molecular self-organization. Furthermore, the detection of the infrared spectroscopic features of such building blocks of life adsorbed on brucite at very low degrees of coverage provides important support to life detection investigations.