Removal of heavy metal ions from aqueous solutions by alkaline-earth metal phosphates

The possibility of utilization of calcium or magnesium phosphates of various composition for heavy and non-ferrous metal extraction from aqueous solutions has been studied. The efficiency of the phosphates in removal of Pb(II), Cr(III) and Fe(III) ions has been shown to decrease in the following sequence: Mg₃(PO₄)₂>MgNH₄PO₄>Ca₃(PO₄)₂>CaHPO₄>Ca₁₀(PO₄)₆(OH)₂ which is inverse to their hydrolytic stability series. It has been established that phosphates of non-apatite structure are capable of binding up to 12 mmol g⁻¹ of the named heavy metals by a chemical interaction. Hydroxyapatite interacts with the polyvalent metal ions via either the above mentioned or ion-exchange mechanism, depending on preparation method used for the apatite and the nature of metal.     

Removal of phosphate from aqueous solution by zeolite synthesized from fly ash

Fifteen Chinese fly ashes were converted hydrothermally into zeolites, and phosphate immobilization capacity (PIC) of the synthesized zeolites and the corresponding raw fly ashes were determined using an initial phosphate concentration of 1000 mg/L. Results showed that there was a remarkable increase in PIC (from 1.2 to 7.6 times) following the synthesis process. Fractionation of immobilized phosphorus indicated that Fe+Al-P increased most significantly and consistently among all the phosphorus fractions following the conversion of fly ash to zeolite. The PIC and Ca+Mg-P were closely related to Ca content (with r values of 0.9683 and 0.9651, respectively) rather than Mg content (with r values of 0.3920 and 0.3212, respectively). The r values of PIC and Fe+Al-P with Fe content (with r values of 0.4686 and 0.6385, respectively) were higher than those with Al content (with r values of -0.7857 and -0.3770, respectively). Although calcium and iron components were mainly involved in phosphate immobilization, there was no significant change of Ca and Fe content following the conversion of fly ash to zeolite. Increase in dissociated Fe(2)O(3) and specific surface area probably accounted for the enhancement in PIC of synthesized zeolites compared with corresponding fly ashes. The PIC value of zeolites showed a significant correlation with dissociated Fe(2)O(3) (r=0.6186). The specific surface area increased 26.0-89.4 times as a result of the conversion of fly ash to zeolite. The maximum removal of phosphate occurred within different pH ranges for zeolites which were synthesized from high, medium and low calcium fly ashes and this behavior was explained by the reaction of phosphate with calcium and iron components.     

Removal of heavy metal ions from aqueous solutions using low-cost sorbents obtained from ash

This study’s main objective was the development of effective low-cost sorbents for the removal of heavy metal ions from aqueous solutions. The influence of different factors on the sorption capacity of ash and modified ash as low-cost sorbents obtained by different methods was investigated. The synthesis of new ash-based materials was carried out at ambient temperature (20°C), 70°C, and 90°C, respectively, in an alkaline medium with NaOH concentrations of 2 M and 5 M, respectively, corresponding to a mixture with solid/liquid ratios of 1: 3 and 1: 5, respectively. The prepared materials (sorbents) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, and BET surface measurement. Adsorption isotherms were determined using the batch equilibrium method. The results showed that these types of new materials displayed a good capacity to remove copper, nickel, and lead ions (29.97 mg of Cu²⁺ per g of sorbent, 303 mg of Ni²⁺ per g of sorbent, and 1111 mg of Pb²⁺ per g of sorbent) from aqueous solutions. The modified materials were prepared using an alkaline attack (a recognised method used in previous studies), but Romanian ash from a thermal power plant was studied for the above purpose for the first time. Hence, the factors which affect the sorption capacity of the prepared low-cost sorbents were determined and their behaviour was explained, taking into account the composition and structure of the new materials.     

Precipitation of magnesium ammonium phosphate from homogeneous solution by means of hydrolysis of p-nitrophenylphosphate with an alkaline phosphatase

In the precipitation of magnesium ammonium phosphate from homogeneous solution, phosphate ions were generated by means of hydrolysis of p-nitrophenylphosphate with an alkaline phosphatase. Conditions for the gravimetric determination of magnesium ion as magnesium ammonium phosphate hexahydrate were investigated.     

Removal of Fe3+ from ammonium dihydrogen phosphate solution in an impact-jet hydraulic cavitation extractor

The impurity of Fe³⁺ in ammonium dihydrogen phosphate (MAP) solution has a significant influence on the morphology and quality of products. The removal of Fe³⁺ from the MAP solution by Di-(2-ethylhexyl) phosphoric acid (D2EHPA) was investigated in an impact-jet hydraulic cavitation (HC) extractor. The organic phase and aqueous phase can be highly mixed under the action of hydraulic cavitation. The extraction efficiency of 80% can be achieved when the extraction reaction was carried out for only 5 min. It was found that the extraction of Fe³⁺ with D2EHPA was an exothermic reaction, and the equilibrium equation of extraction was obtained by slope method as follows: $F{e}_{(aqu)}^{3+}+8{\left(\mathit{HD}\right)}_{2(org)}={\left(\mathit{Fe}{D}_3·13HD\right)}_{(org)}+3H_{(aqu)}^{+}$After the two-stage extraction, the extraction efficiency of up to 96.7% can be reached (only 3.4 ～ 4 ppm Fe³⁺ remained in the aqueous phase), and the MAP crystals with regular polyhedral structure, single phase nature, and high optical transmittance were obtained.     

Heavy metal immobilization in aqueous solution using calcium phosphate and calcium hydrogen phosphates

This study examines the possibilities for removing heavy metal cations from water with calcium phosphate, calcium hydrogen phosphate, and calcium dihydrogen phosphate at 293 K. It was reported that immobilization of aqueous heavy metal cations, which is known to be one of the characteristic properties of calcium hydroxyapatite, proceeded favorably with these phosphates. Calcium phosphate, calcium hydrogen phosphate, and calcium dihydrogen phosphate could favorably remove Pb2+ from aqueous solution. Calcium hydrogen phosphate also removed aqueous Cu2+, Co2+, and Cd2+, whereas these cations were not immobilized by calcium phosphate and calcium dihydrogen phosphate. A contribution of the dissolution-precipitation mechanism to immobilization with these phosphates is suggested.     

Thermal parameters of undoped and medicines doped calcium hydrogen phosphate dihydrate and magnesium ammonium phosphate hexahydrate crystals

Journal of Thermal Analysis and Calorimetry - In the present study, undoped and medicines doped Calcium Hydrogen Phosphate Dihydrate and Magnesium Ammonium Phosphate Hexahydrate crystals are grown...     

Removal of sulphate and phosphate from aqueous solutions using a food grade polysaccharide as flocculant

The mucilage extracted from the seeds of Tamarindus indica pods, a food grade natural polysaccharide, is used as a flocculant for removal of sulphate and phosphate ions in aqueous medium. The maximum removal obtained was 73.71% for sulphate ions and 75.71% for phosphate ions after 30 min. The optimum mucilage dose was 50 mg/L for both sulphate and phosphate ions. The maximum removal was obtained at acidic pH for both the ions. A series of contact time experiments were conducted to assess the system variables such as concentrations of mucilage and ions and pH. The conductivity measurements were also done and correlated with the percent removal. This eco-friendly food grade polysaccharide was proved to be a very good flocculant for the removal of sulphate and phosphate ions.     

Reaction of magnesium oxide and magnesium silicates with ammonium hydrodifluoride

The reactions of magnesium oxide and magnesium silicates (forsterite and serpentines) with ammonium hydrodifluoride is studied using DTA, X-ray powder diffraction, and IR spectroscopy. The conditions for the formation of intermediate phases are determined. The structure of the silicate mineral does not significantly affect the fluorination.     

Removal of ammonium ion from aqueous solutions using natural zeolite: kinetic,equilibrium and thermodynamic studies

The aim of the present study is to investigate the removal of ammonium ions from aqueous solutions using the natural Western Azerbaijan zeolite by utilizing ion exchange process. Batch experimental studies were conducted to evaluate by changing relevant parameters such as pH, dosage of adsorbent, stirring time, initial ammonium concentration, and temperature. The results clearly confirmed that all mentioned parameters have vital affects on removing ammonium ions from wastewater and effluents, so got optimized. Adsorption kinetics and equilibrium data for the removal of ammonium ion were analyzed using Langmuir and Freundlich equations. The Langmuir model fits the equilibrium data better than the Freundlich model. According to the Langmuir equation, the maximum uptake for ammonium ion was 43.47 (mg g^?1). Pseudo-first-order and pseudo-second-order models were used to represent the kinetics of the process. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicate that the adsorption process is feasible, spontaneous, and endothermic at 20–50 °C. Based on the experimental results, it can be suggested that the natural Western Azerbaijan zeolite has the potential of application as an efficient adsorbent for the removal of ammonium ions from aqueous solutions, and is suggested for wastewater treatment purposes.     

Precipitation of zinc ammonium phosphate from homogeneous solution

Urea hydrolysis has been employed to raise the pH for homogeneous precipitation of zinc ammonium phosphate. From 30 to 100 mg of zinc can conveniently be determined by this technique (relative standard deviation 0.2% for 89 mg). The interference of nickel was minimized by using ammonium tartrate as masking agent, but copper could not be effectively masked with the same tartrate. Ammonium tartrate obtained from a different source was found to mask the copper more effectively. Investigations showed that the latter tartrate contained an appreciable amount of ammonium oxalate.     

Precipitation of manganese ammonium phosphate from homogeneous solution

Precipitation of manganese, zinc and cadmium ammonium phosphates from homogeneous solution by decomposition of metal EDTA complexes by boiling with hydrogen peroxide in presence of phosphate has been investigated. Precipitation of Cd is not quantitative, but of Mn is complete in 2 hr, and of Zn in 6 hr.     

Hydrated ammonium manganese phosphates by electrochemically induced manganese-defect as cathode material for aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) with the merits of low cost, low toxicity, high safety, environmental benignity as well as multi-valence properties as the large-scale energy storage devices demonstrate tremendous application prospect. However, the explorations for the most competitive manganese-based cathode materials of AZIBs have been mainly limited to some known manganese oxides. Herein, we report a new type of cathode material NH₄MnPO₄·H₂O (abbreviated as AMPH) for rechargeable AZIBs synthesized through a simple hydrothermal method. An in-situ electrochemical strategy inducing Mn-defect has been used to unlock the electrochemical activity of AMPH through the initial charge process, which can convert poor electrochemical characteristic of AMPH towards Zn²⁺ and NH₄⁺ into great electrochemically active cathode for AZIBs. It still delivers a reversible discharge capacity up to 90.0 mAh/g at 0.5 A/g even after 1000^th cycles, which indicates a considerable capacity and an impressive cycle stability. Furthermore, this cathode reveals an (de)insertion mechanism of Zn²⁺ and NH₄⁺ without structural collapse during the charge/discharge process. The work not only supplements a new member for the family of manganese-based compound for AZIBs, but also provides a potential direction for developing novel cathode material for AZIBs by introducing defect chemistry.     

Preparation of magnesium hydroxide from nitrate aqueous solution

Nucleation of Mg(OH)₂ was investigated by measuring the electrical conductivity and pH of the Mg(NO₃)₂ reaction solution to which ammonia containing different amounts of NH₄NO₃ was added. NH₄NO₃ increases solubility and slows down precipitation of Mg(OH)₂ in the system. Data are presented on the influence of NH₄NO₃ on the solubility of Mg(OH)₂ at 25°C. The phenomena observed can be explained by the solvation effect of nitrate ions brought to the system with the addition of ammonium nitrate, which was proved by NMR spectroscopy. When the mass fraction of NH₄NO₃ exceeds 15 %, homogeneous nucleation does not proceed. It was found that seeding of the system with Mg(OH)₂ crystals only influenced the rate of Mg(OH)₂ crystallisation, not the size and shape of the crystals. Primary crystals are smaller than 0.1 μm. The large difference in the surface energy of individual crystal planes leads to oriented agglomeration. This process is accelerated in a pressure reactor at 130°C. The resulting polycrystals are hexagonal plates 0.2 μm thin with a diameter of 1–2 μm. Under variable reaction conditions, agglomerates as big as 30 μm can be prepared.     

Sodium, ammonium, calcium, and magnesium forms of zeolite Y for the adsorption of glucose and fructose from aqueous solutions

The kinetics of adsorption by sodium, ammonium, calcium and magnesium forms of zeolite Y from aqueous solutions containing 25% w/v of either one or an equimolar mixture of glucose (G) and fructose (F) have been studied batch-wise at 50 degrees C. The adsorption of aqueous pure G was fast, while that of aqueous pure F depended on the cationic form, approaching that of G on the Mg-Y, and slowing down in the sequence of Mg2+ > NH4+ > Ca2+ > Na+ of the cations. The adsorption behavior from solutions containing both G and F indicated significant hindering effects of F on G on Na-Y. Na-Y and Mg-Y did not exhibit rate-based selectivity, while Ca-Y an NH4-Y adsorbed G faster than F. Addition of CaCl2 to the mixture of Ca-Y and aqueous solution of G and F improved the separation, by hindering the adsorption of F. Addition of NH4Cl to the mixture of the sugar solution and NH4-Y, on the other hand, had a negative effect on the separation. NH4-Y was found to be desorbing about 30% of the adsorbed sugars and this value was found to be around 50% for Ca-Y. Re-adsorption experiments resulted in similar or somewhat higher percentages of amounts adsorbed compared to adsorption on fresh samples. Both NH4-Y and Ca-Y were found to be re-adsorbing around 50% of the sugars they adsorbed on fresh samples.