Performance of Nano Zero-Valent Iron Derived from the Decomposition of Siderite in the Removal of Phosphate.

Natural siderite was selected as a raw material for preparing nano zero-valent iron (nZVI). The efficiency of the as-synthesized nZVI for PO3-4-P removal was investigated, and the effects of the annealing temperature, pH, initial PO3-4-P concentration, adsorption temperature and oxygen were investigated. The results indicated that after annealing at 550 °C, nZVI exhibited an average crystal size of 56.3 nm and a surface area of 14.1 m²/g. A decrease in pH and an increase in oxygen availability enhanced the removal efficiency. The adsorption process, which was spontaneous and exothermic according to the thermodynamic analysis, agreed well with the pseudo-second-order kinetic model. Based on the Langmuir equilibrium isotherms, the capacity of nZVI to adsorb phosphorus was determined to be 33.18 mg/L. The optimized conditions for the experimental conditions were defined by an orthogonal experiment as follows: initial P concentration 2 mg/L, initial pH 4, iron dose 2 g/L, adsorption time 60 min. The experimental results suggested that the as-prepared nZVI was a promising adsorbent for the removal of phosphate.

Simultaneous removal of nitrate and phosphate from wastewater by siderite based autotrophic denitrification.

The potential of simultaneous removal of nitrate and phosphate from wastewater by a single anaerobic Fe(II) oxidizing denitrifiers (the strain PXL1) was assessed using siderite biofilters under different influent TOC concentrations and hydraulic retention times (HRTs) over a 160-day trial. Higher TOC concentrations promoted NO3- removal, while there was no significant influence on PO43- removal. Lowering down HRT from 10 h to 5 h did not significantly influence NO3- and PO43- removal. The NO3- removal performance and microbial community structure in the biofilters indicated that NO3- was reduced to N2 by both strain PXL1 and heterotrophic Acidovorax delafieldii. Iron content analysis of the used siderite along the biofilters showed that PO43- removal was improved by the bio-oxidation of Fe(II) in siderite to Fe(III) via the strain PXL1. The coexistence of the strain PXL1 and natural siderite in nitrate-contaminated aquifers provides a practical technology for in situ remediation of nutrient contaminated waterbodies.

Goethite promoted biodegradation of 2,4-dinitrophenol under nitrate reduction condition.

Iron oxide may interact with other pollutants in the aquatic environments and further influence their toxicity, transport and fate. The current study was conducted to investigate the biodegradation of 2,4-dinitrophenol (2,4-DNP) in the presence of iron oxide of goethite under anoxic condition using nitrate as the electron acceptor. Experiment results showed that the degradation rate of 2,4-DNP was improved by goethite. High performance liquid chromatography-mass spectra analysis results showed that goethite promoted degradation and transformation of 2,4-diaminophenol and 2-amino-4-nitrophenol (2-nitro-4-aminophenol). Microbial community analysis results showed that the abundance of Actinobacteria, which have the potential ability to degrade PAHs, was increased when goethite was available. This might partially explain the higher degradation of 2,4-DNP. Furthermore, another bacterium of Desulfotomaculum reducens which could reduce soluble Fe(III) and nitrate was also increased. Results further confirmed that nanomaterials in the aquatic environment will influence the microbial community and further change the transformation process of toxic pollutants.

[Preparation of Magnetic Biomass Carbon by Thermal Decomposition of Siderite Driven by Wheat Straw and Its Adsorption on Cadmium].

C-Fe3O4 composite material [magnetic biomass char (MBC)] was prepared by pyrolysis of a mixture of wheat straw and siderite at 500℃. The MBC was characterized by XRF, FTIR, XRD, SEM, XPS, and a magnetic susceptibility device. The effect of contact time, pH value, initial Cd2+ concentration, and ionic strength on the adsorption capacity of the MBC to Cd2+ was investigated. The results showed that the BET surface areas of the MBC and biomass char (BC) were 23.38 m2·g-1 and 7.20 m2·g-1, respectively, total pore volumes were 1.04×10-1 cm3·g-1 and 2.23×10-2 cm3·g-1, and average pore diameters were 17.74 nm and 12.38 nm. The magnetic susceptibility of the MBC was 42900×10-8 m3·kg-1. FTIR showed that phenolic hydroxyl and carboxyl functional groups bound metal ions on the surface of the MBC and BC. The kinetic data of the MBC were described well by the pseudo-second-order model. Isothermal adsorption of Cd2+ by MBC and BC was fitted well by the Freundlich equation. The adsorption velocity increased with an increase of pH in the region 3-6 and then stabilized in the region 6-9. The adsorption capacity of Cd2+ decreased slightly when ionic strength increased from 1 mmol·L-1 to 100 mmol·L-1, whereas the desorption rate increased from 0.51% to 8.5%. The adsorption properties and characterization results illustrated that the removal mechanism of Cd2+ likely was through adsorption and ion exchange on the surface of the MBC with a high amount of functional groups. In addition, magnetic adsorbents offered a significant advantage compared to other adsorbents in the aspect of separation from aqueous solution.

Synthesis of calcium carbonate using extract components of croaker gill as morphology and polymorph adjust control agent.

Biomimetic synthesis of calcium carbonate with various polymorphs, sizes and morphologies by using organic substrates has become an interesting topic for the last years. Calcium carbonate has been synthesized by the reaction of Na2CO3 and CaCl2 in the presence of extract components of croaker gill. The products were characterized by powder X-ray diffraction (PXRD) and Fourier transform infrared (FT-IR) spectrum, and particle morphologies were observed by scanning electron microscope (SEM). The results show that at lower concentration yellow croaker gill extract has no effect on calcium carbonate crystal polymorph. Calcite was obtained only. But the morphologies of calcite particle change with the increase of the concentration. The corners of the particle change from angular to curved. However, with the further increase of the concentration of yellow croaker gill extract, the calcium carbonate obtained is a mixture of calcite and vaterite. The vaterite component in the mixture rises with increasing concentration of extract solution, indicating that the proteins from the yellow croaker gill during growth play a crucial role in stabilizing and directing the crystal growth.

Biomimetic synthesis of hollow calcium carbonate with the existence of the agar matrix and bovine serum albumin.

Proteins play important roles in the process of biomineralization. Vaterite and calcite have been synthesized by the reaction of Na2CO3 and CaCl2 in the bovine serum albumin (BSA) and agar system. The samples have been characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The shape of CaCO3 crystal has been analyzed by scanning electronic microscopy (SEM). The results show that calcite is a single product in the absence of BSA, but the product is a mixture of calcite and vaterite in the presence of BSA. The spheral shell of CaCO3 crystal was obtained when the concentration of BSA increased to 9.0mg/mL.

Confirmation of the assignment of vibrations of goethite: an ATR and IES study of goethite structure.

Transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM/EDS) and X-ray diffraction (XRD) were used to characterize the morphology of synthetic goethite. The behavior of the hydroxyl/water molecular units of goethite and its thermally treated products were characterized using Fourier transform-infrared emission spectroscopy (FT-IES) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The results showed that all the expected vibrational bands between 4000 and 650 cm(-1) including the resolved bands (3800-2200 cm(-1)) were confirmed. A band attributed to a new type of hydroxyl unit was found at 3708 cm(-1) and assigned to the FeO-H stretching vibration without hydrogen bonding. This hydroxyl unit was retained up to the thermal treatment temperature of 500 °C. On the whole, seven kinds of hydroxyl units, involving three surface hydroxyls, a bulk hydroxyl, a FeO-H without hydrogen bonding, a nonstoichiometric hydroxyl and a reversed hydroxyl were observed, and three kinds of adsorbed water were found in/on goethite.

Effect of rehydration on structure and surface properties of thermally treated palygorskite.

Palygorskite has a fibrous like morphology with a distinctive layered appearance. The simplified formula of palygorskite (Mg(5)Si(8)O(20)(OH)(2)(OH(2))(4)·nH(2)O) indicates that two different types of water are present. The dehydration and rehydration of palygorskite have been studied using thermogravimetry and H(2)O-temperature programmed desorption. X-ray diffractograms, NH(3) adsorption profiles, and NH(3) desorption profiles were obtained for thermally treated palygorskite as a function of temperature. The results proved water molecules were mainly derived from Si-OH units. In addition, five kinds of acid sites were found for palygorskite. The number of acid sites of external surfaces was larger than that of the internal surfaces. Bonding on the internal surface acid sites was stronger than the bonding of the external surfaces. Rehydration restored the folded structure of palygorskite when thermal treatment temperature was lower than 300 °C.

Effect of aging time and Al substitution on the morphology of aluminous goethite.

Goethite and Al-substituted goethite were synthesized from the reaction between ferric nitrate and/or aluminum nitrate and potassium hydroxide. XRF, XRD, TEM with EDS were used to characterize the chemical composition, phase and lattice parameters, and morphology of the synthesized products. The results show that d(020) decreases from 4.953 to 4.949Å and the b dimension decreases from 9.951Å to 9.906Å when the aging time increases from 6 days to 42 days for 9.09 mol% Al-substituted goethite. A sample with 9.09 mol% Al substitution in Al-substituted goethite was prepared by a rapid co-precipitation method. In the sample, 13.45 mol%, 12.31 mol% and 5.85 mol% Al substitution with a crystal size of 163, 131, and 45 nm are observed as shown in the TEM images and EDS. The crystal size of goethite is positively related to the degree of Al substitution according to the TEM images and EDS results. Thus, this methodology is proved to be effective to distinguish the morphology of goethite and Al substituted goethite.

[Denitrification water treatment with zeolite composite filter by intermittent operation].

The zeolite composite filters (ZCF) with the size of4-8 mm were prepared using raw zeolite (0.15-0.18 mm) as the main material and the cement as binder. After a combination of material characterizations, such as the void fraction, apparent density, compression strength and surface area, the optimal prepared conditions of composite filters were obtained as follow: weight ratio of m (zeolite): m (cement) = 7 : 3, curing for 15 d under the moisture condition and ambient temperature. Through upflow low-concentration ammonia nitrogen wastewater, ZCF filled in the experimental column was hung with the biological membrane. Thus, intermittent dynamic experiments were conducted, the intermittent operation cycle included adsorption, biological regeneration and drip washing. Until concentration of ammonia nitrogen was more than 2 mg x L(-1) of effluent standards, water in experiment column was firstly emptied, and then blast biological regeneration was conducted. After the filters were bathed with water, the zeolite adsorption-biological regeneration cycle was performed repeatedly. The experimental results show that under conditions of 24 h blast and 5 d of continuous operation period, ammonia nitrogen removal rate is up to 87.6% on average, total nitrogen removal rate reaches 51.2% on average.