The flotation separation of apatite from dolomite using a fatty acid-based collector and the mechanisms of adsorption

In this work, GJBW, a fatty acid-based agent, was used as an efficient collector to separate dolomite from apatite to achieve high-purity apatite. The flotation performance of dolomite and apatite in the phosphate (H₃PO₄) system treated with sodium oleate (NaOl) and GJBW, respectively, was studied and compared. Microheat tests, surface characterization, and flotation solution chemistry calculations were used to evaluate the adsorption mechanism of GJBW onto dolomite. The smoothness and flatness of dolomite treated and untreated with GJBW may be also detected via atomic force microscopy (AFM). Microflotation results illustrated that GJBW performed better than NaOl for separating apatite from dolomite under the H₃PO₄ system. The grade of P₂O₅ in concentrates treated with 10 mg/L GJBW was 31.49%, which was 4.98% higher than that of NaOl. The recovery rate of P₂O₅ was 87.05%, which was 4.71% higher than that of NaOl. Microheat tests demonstrated that GJBW generated a higher heat of adsorption onto dolomite than did the same concentration of NaOl, significantly enhancing the dolomite's hydrophobicity. Fourier transform infrared spectroscopy (FTIR), zeta potential, flotation solution chemistry calculations, and surface characterization further demonstrated that GJBW may ionize large amounts of RCOO⁻ and H (RCOO)²⁻ ions in solution, which can be significantly chemisorbed with numerous sites of Ca and Mg exposed to dolomite, forming dense point-like adsorption onto dolomite. These findings shed more light on the mechanism of interaction between GJBW and dolomite, which has profound implications for the study and use of fatty acid-based treatments in phosphate ores.     

The Effect of Oleic Acid Emulsification using SPE on Fluorite and Dolomite Flotation**

Collector OA, oleic acid, is widely used industrially for fluorite flotation. Low selectivity, dispersibility and collecting capability of the OA collector are always observed. In this study, compared with flotation of dolomite, a collector mixture of OA and SPE (styrylphenol polyoxyethylene ether) demonstrated significantly better performances for the fluorite. An optimal mass ratio 4 : 1 OA : SPE was found, and the recovery of fluorite was increased from over 85 % to more than 94 % compared with pure OA. Furthermore, the dosage of the collector agent was reduced from 50 mg mL⁻¹ to 20 mg mL⁻¹, which did not negatively impact the recovery of dolomite. The results from the contact angle tests indicated that SPE selectively increased the surface hydrophobicity of fluorite but had little effect on dolomite. Besides, zeta potential measurements and IR analyses revealed that the addition of SPE led to strong chemical adsorption on the surface of fluorite, resulting in a significant difference in the flotation performances of the two minerals. Therefore, SPE-emulsified OA is corroborated to prompt more selectivity and collecting capability on flotation of fluorite over dolomite.     

Experimental and theoretical studies of media effects on copper corrosion in acidic environments containing 2-amino-5-mercapto-1,3,4-thiadiazole

Corrosion behaviour of copper metal in acid solutions (HCl, H₂SO₄ and H₃PO₄) containing 2-amino-5-mercapto-1,3,4- thiadiazole (AMT) was investigated experimentally and theoretically via gravimetric, potentio-dynamic and quantum electrochemical approaches. Similar behavior was observed for H₂SO₄ and H₃PO₄ media, and related to the nature of anions at metal/solution interface. With regard to HCl, however, the rate of corrosion was determined to be low at initial stages, but high later on using an auto-catalyzing mechanism. In the presence of AMT, the experimental studies revealed that this molecule was a good anodic-type inhibitor causing substantial changes in corrosion potential. Moreover, its adsorption obeys the Langmuir isotherm. The values of ΔG _ads were determined and correlated to the inhibitor powers. Finally, the influence of media (anions) on metal corrosion was also investigated from molecular point of view by calculations of the copper-anions interaction using density functional theory.     

Studies on the removal of phosphate in water through adsorption using a novel Zn-MOF and its derived materials

A novel zinc-based metal–organic framework, {[Zn₃(atz)₂(pda)₂]·2(H₂O)}_n (Zn-MOF; Hatz is 5-aminote-1H-terazole; H₂pda is malonic acid), was prepared using the solvothermal method. Carbonization of the prepared Zn-MOF was conducted under elevated temperatures to investigate its phosphate adsorption performance. Through pre-adsorption experiments, the optimal carbonization temperature of 500 °C was determined, yielding Zn-MOF-500. Besides, multiple characterization methods were used to analyze the properties of Zn-MOF and Zn-MOF-500 materials before and after the adsorption of phosphate ions. The results showed that the BET surface area of Zn-MOF-500 was 18.57 m²/g, which was 16.37 times larger than that of the BET surface area of Zn-MOF. At 25 °C, Zn-MOF and Zn-MOF-500 exhibited an adsorption capacity of 123.44 and 226.07 mg/g, respectively. Based on the adsorption isotherms and the adsorption kinetics, the adsorption of PO₄^3- occurs via monolayer. X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS) analysis showed that P was adsorbed on Zn-MOF and Zn-MOF-500 as the zinc hydrogen phosphate and zinc phosphate ions, respectively.     

Removal of phosphate from solution by adsorption and precipitation of calcium phosphate onto monohydrocalcite

The sorption behavior and mechanism of phosphate on monohydrocalcite (CaCO₃?H₂O: MHC) were examined using batch sorption experiments as a function of phosphate concentrations, ionic strengths, temperatures, and reaction times. The mode of PO₄ sorption is divisible into three processes depending on the phosphate loading. At low phosphate concentrations, phosphate is removed by coprecipitation of phosphate during the transformation of MHC to calcite. The sorption mode at the low-to-moderate phosphate concentrations is most likely an adsorption process because the sorption isotherm at the conditions can be fitted reasonably with the Langmuir equation. The rapid sorption kinetics at the conditions is also consistent with the adsorption reaction. The adsorption of phosphate on MHC depends strongly on ionic strength, but slightly on temperature. The maximum adsorption capacities of MHC obtained from the regression of the experimental data to the Langmuir equation are higher than those reported for stable calcium carbonate (calcite or aragonite) in any conditions. At high phosphate concentrations, the amount of sorption deviates from the Langmuir isotherm, which can fit the low-to-moderate phosphate concentrations. Speciation–saturation analyses of the reacted solutions at the conditions indicated that the solution compositions which deviate from the Langmuir equation are supersaturated with respect to a certain calcium phosphate. The obtained calcium phosphate is most likely amorphous calcium phosphate (Ca₃(PO₄)₂?xH₂O). The formation of the calcium phosphate depends strongly on ionic strength, temperature, and reaction times. The solubility of MHC is higher than calcite and aragonite because of its metastability. Therefore, the higher solubility of MHC facilitates the formation of the calcium phosphates more than with calcite and aragonite.     

Adsorption of N-tallow 1,3-propanediamine-dioleate collector on albite and quartz minerals, and selective flotation of albite from greek stefania feldspar ore

The adsorption behavior of tallow 1,3-propanediamine-dioleate (Duomeen TDO) collector on albite and quartz minerals is assessed through Hallimond flotation, zeta potential, and diffuse reflectance FTIR investigations, together with the species distribution of the collector. The collector performance on albite separation from a natural feldspar material is evaluated in bench scale flotation tests. The Hallimond flotation responses of the minerals as a function of pH and collector concentration indicate that albite can be selectively floated from quartz at pH 2 where the doubly positively charged collector species adsorb on albite but not on quartz. However, the zeta potential and infrared spectra reveal that the adsorption behavior of the collector is similar on both minerals. The discrepancy in the flotation and adsorption results is attributed to the coarse and fine particle size fractions, and the shorter and longer equilibration periods employed in these studies respectively. The comparable adsorption on fine particles of albite and quartz at pH 2 is explained by the interaction of ammonium ions on silanol groups by hydrogen bonding as well as electrostatic interactions. The changes in zeta potentials are in good agreement with the formation of ionic species and free molecular forms of the collector. The IR spectra show the coexistence of neutral oleic acid together with charged amine species at low pH values in accordance with the species distribution diagram. Selective flotation of albite is accomplished from a natural feldspar material with tallow diamine-dioleate collector at pH 2 using sulfuric acid, only when the feed is deslimed prior to the bench scale flotation tests. An albite recovery exceeding 85% is achieved from a feed material containing about 50% albite.     

A rapid volumetric method for the determination of beryllium in beryls and associated minerals

A new volumetric method has been proposed for the determination of beryllium in beryls and associated minerals. The method involves the direct precipitation of beryllium as BeNH₄PO₄.6H₂O in presence of complexone II, dissolving the precipitate in dilute perchloric acid and titrating the liberated phosphate with standard bismuthyl perchlorate. Results for samples agree within ± 0.2% of the standard values.     

Adsorption,Thermodynamic, and Experimental Studies of Corrosion Inhibitor of Tin in 0.2 M Maleic Acid by Hydrogen Phosphate Ions (HPO42−)

The inhibition efficiency of H₂PO₄²⁻ ions against tin corrosion in 0.2 M maleic acid is studied using electrochemical methods, surface analytical methods, and thermodynamic analysis. The potentiodynamic polarization plots showed the presence of an active/passive transition state of the tin electrode. The EIS measurements confirmed that the inhibition efficiency of H₂PO₄²⁻ increased by increasing the concentration (η=81 % at C_inh=2.10⁻² M) and decreased by rising the temperature. The polarization tests demonstrated that the inhibitor performs as a cathodic-type. The adsorption of the inhibitor was spontaneous and followed the Langmuir adsorption isotherm. A model of the inhibition mechanism was suggested.     

Hydroclathrus clathratus marine alga as a green inhibitor of acid corrosion of mild steel

The corrosion inhibitive and adsorption behaviors of Hydroclathrus clathratus on mild steel in 1 M HCl and 1 M H₂SO₄ solutions at 303, 313 and 323 K were investigated by weight loss, electrochemical, and surface analysis techniques. The results show that H. clathratus acts as an inhibitor of corrosion of mild steel in acid media. The inhibition efficiency was found to increase with increase in inhibitor concentration but to decrease with rise in temperature, suggestive of physical adsorption. The adsorption of the inhibitor onto the mild steel surface was found to follow the Temkin adsorption isotherm. The inhibition mechanism was further corroborated by the results obtained from electrochemical methods. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses supported the inhibitive action of the alga against acid corrosion of mild steel.     

Influence of maturation conditions of hydroxyapatite gel on the composition of xerogel

The influence exerted by conditions of the secondary maturation of hydroxyapatite gel on the composition of a xerogel was determined. It was found that the prolonged stage of the secondary maturation within pH 7.6–7.1, the low pH value of distilled water or a solution of the acid (HCl, H₃PO₄) and the long time of contact of the hydoxyapatite gel with the acid solution assist the formation of α-tricalcium phosphate impurity. A singlephase hydroxyapatite is formed in the presence of distilled water with pH 5.3–5.6, as the time of the secondary stage of maturation of hydroxyapatite gel within pH 7.6–7.1 is decreased and the total washing time is decreased up to 34–40 days.     

Zinc Recovery from Wulagen Sulfide Flotation Plant Tail by Applying Ether Amine Organic Collectors

Separating oxidized zinc minerals from flotation tailings is always a challenge. In this study, a flotation tailing from Wulagen zinc mine in China (Zn grade < 1%) was processed using froth flotation with combinations of amines (OPA 10, OPA 1214, OPA 13, DDA) and Na₂S to study the effects of these amines on the zinc recovery as well as their interactions with other reagents, aiming to screen out a proper reagent scheme to improve zinc separation from extremely low-grade zinc flotation tailings. The results show that different amines led to different flotation performance, and the collectors were ranked as OPA 1214, OPA 13, OPA 10 and DDA in a decreasing order based on flotation collectivity and selectivity. An increase in the concentration of each collector increased the zinc recovery but reduced the concentrate zinc grade. Interactions were also observed between different amines and Na₂S and Na₂SiO₃, and OPA 1214 outdid the others in saving the usage of both the Na₂S and Na₂SiO₃. The measured adsorption of collector onto smithsonite was found to correlate well with flotation test results. It was concluded that hydrocarbon chains can be held accountable for the difference in the flotation performance with different amines. The longer the hydrocarbon chain, the stronger the hydrophobic association ability of amine, which is conducive to the selective amine adsorption onto sulfurized smithsonite particles and hence the smithsonite flotation.     

Spirulina platensis – A novel green inhibitor for acid corrosion of mild steel

The inhibition of the corrosion of mild steel in 1 M HCl and 1 M H₂SO₄ by Spirulina platensis has been studied at different temperatures viz., 303 K, 313 K and 323 K by weight loss method, potentiodynamic polarization method, electrochemical impedance spectroscopy measurements and SEM analysis. The inhibition efficiency increased with increasing concentration of the inhibitor in both HCl and H₂SO₄ media. The results of weight loss studies correlated well with those of impedance and polarization studies. From the results of weight loss studies at various temperatures, the mode of adsorption is confirmed to be physisorption. Further the adsorption has been found to follow Temkin isotherm. From this isotherm, the free energy of adsorption (ΔG) and entropy (ΔS) are calculated. The study reveals the corrosion inhibition potential of S. platensis in both the acid media, thus bringing to light another facet of this microalga as it has so far been used only to produce antioxidant principles, finding extensive use in medicine especially as neutraceutical.     

Detection of metaphosphate intermediates in reaction solutions of phosphate esters: Chromatographic and spectroscopic studies

This study was undertaken to gain a better understanding of uncatalysed phosphoryl transfer reactions under neutral pH conditions in aqueous media. A combination of chromatographic (Ultra high performance liquid chromatography, UHPLC) and spectroscopic (Quadrupole time-of-flight-mass spectrometry- qTOF-MS;) UV-vis; and FTIR techniques were utilized to probe the mechanism of reaction under physiological conditions (aqueous medium; pH 7.0; 25°C). Mass spectroscopic data from these studies reveal that the phosphate monoesters, phenyl phosphate (PP) and 4-nitrophenyl phosphate (NPP) undergo collision-induced dissociation dynamics through the formation of the metaphosphate intermediate, [PO₃]^? – m/z 79, a process that was found to be independent of the pKa of the leaving group. Under conditions of the present experiment, the metaphosphate intermediate does not undergo protonation to either metaphosphoric acid, HPO₃ or the dibasic phosphonic acid, H₃PO₃.     

Enthalpimetric and Colorimetric Determinations of the Inhibition Constant for the Inhibition of Urease by Boric Acid

Continuous enthalpimetric and fixed-time-point colorimetric analytical studies of jack bean urease-catalyzed hydrolysis of urea uninhibited and inhibited by boric acid were performed. The effect of boric acid on urease activity was studied in 100 mM phosphate buffer of pH 7 (H₃PO₄+NaOH, 2 mM EDTA) at 25°C. The inhibition constant of boric acid was obtained with use of differential and integration methods. It was found that boric acid is a simple competitive inhibitor of urease. The methods produced comparable values of the inhibition constant K_i: the former 0.19 mM and the latter 0.18 mM. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrochemical polymerization of aniline in phosphoric acid

The electrochemical synthesis of common conductive polymers such as polyaniline in phosphoric acid is a little different from that in other acidic media such as sulfuric acid. Electropolymerization in phosphoric acid is difficult, and this electrolyte medium is not applicable for this purpose. However, it is possible to overcome this problem by the addition of a small amount of sulfuric acid. In this case, the electropolymerization process can be successfully performed when the phosphate ion is doped. For instance, polyaniline films electrodeposited from an electrolyte solution of phosphoric acid have good stabilities and useful morphologies. Interestingly, phosphate doping results in the formation of nanostructures, whereas the polymer surface is macroscopically smooth. In an appropriate ratio, a mixed electrolyte of H₃PO₄ and H₂SO₄ can be used for the electropolymerization of aniline; thus, H₂SO₄ acts as a required agent for successful polymer growth, and H₃PO₄ acts as a doping agent. In this case, a small amount of sulfate is incorporated into the polymer matrix, which does not participate in the electrochemical insertion/extraction process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3304–3311, 2006     

Study of composition and structure of aluminum phosphate binder

In this article, theoretical analysis and different testing techniques were used to study the reaction pathways and synthesized products of phosphoric acid and aluminum hydroxide at different Al/P molar ratios. The results show that: (a) When the molar ratio of phosphoric acid/aluminum hydroxide is 1:3, the reaction will produce stoichiometric aluminum dihydrogen phosphate (Al(H₂PO₄)₃); (b) when Al(OH)₃ is excessive, an intermediate, monohydroxy aluminum dihydrogen phospate (HO-Al-(H₂PO₄)₂), will appear, which is unstable and will continue to react according to two reaction pathways, one is intramolecular dehydration to form phosphoric acid hydrogen-dihydrogen aluminum diphosphate (H₂PO₄)Al(HPO₄); the other is intermolecular dehydration cross-linking to form a polymeric macromolecular aluminum phosphate H-((HPO₄)(H₂PO₄)Al-O-HPO₄-Al(H₂PO₄)-O)- _nH. The ratio of the two pathways is affected by the excess of Al(OH)₃. When the excess of Al(OH)₃ continues to increase, the ratio of the second reaction path begins to increase and the viscosity of the product gradually increases. Adhesion experiments show that the aluminum dihydrogen phosphate has the best bonding performance benefiting from its lower viscosity.     

Radiotracer study of the adsorption of phosphoric acid on platinized platinum electrodes in the presence of different ions and oxalic acid

Radiotracer study of the adsorption of phosphoric acid on platinized platinum electrodes was carried out under different experimental conditions. The potential and concentration dependence of the adsorption was studied at low concentrations (5×10^?6–6×10^?3 mol dm^?3) in the presence of 1 M HClO₄ supporting electrolyte. A Freundlich type isotherm was found. The effect of different additives was studied. In the presence of Cl^? and HSO₄^? ions and oxalic acid the decrease of the adsorption of H₃PO₄ may be observed. On the other hand Cd²⁺ and Cu²⁺ ions induce the increase of the adsorption of H₃PO₄ in the potential range where their electrosorption takes place.     

Monte Carlo simulation and electrochemical performance corrosion inhibition whid benzimidazole derivative for XC48 steel in 0.5 M H2SO4 and 1.0 M HCl solutions

The inhibition of 1-(4-methoxybenzyl)-2-(4-methoxyphenyl)-1H-benzimidazole (MMB) on corrosion of XC48 steel in solutions 1.0 M HCl and 0.5 M H₂SO₄ were studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques (EIS). Potentiodynmic polarization curves revealed that MMB acts as a mixed-type inhibitor in both acidic media. The impedance results indicated that the corrosion process occurs under activation control. Furthermore, MMB shows a higher inhibition efficiency in HCl (97%) than in H₂SO₄ (92%) at 10^?4 M MMB. The values of ΔG°_ads, ΔH_a, E_a and ΔS_a in temperature range 293–323 K indicated that MMB strongly retarded the corrosion of XC48 steel in both solutions by a chemisorptions process. The adsorption of Benzimidazole (MMB) on carbon steel surface followed Langmuir adsorption isotherm. Scanning electron microscopy (SEM) analysis confirmed that there is an adsorbed film on the surface of XC48 steel. The results of Monte Carlo simulations studies confirmed the inhibition action of MMB.     

Confined space effects driving to heterogenization of solutions at the interfaces

Water and concentrated solutions of acids (HCl, H₃PO₄, and H₃PO₃) or H₂O₂ are clustered at the interfaces of nanosilicas and multi-layer graphene oxide (MLGO) as shown by low-temperature ¹H NMR spectroscopy. The acid solutions in contact with silica or MLGO powders placed in nonpolar (CCl₄) or weakly polar (CDCl₃) media form nanodomains and clusters of several types and sizes with different contents of water and solutes. This differentiation of the solutions is stronger at a surface of more compacted nanosilicas because of enhanced confinement effects in narrower pores (voids) between adjacent nanoparticles. For MLGO, the confined space effects are relatively weak but the formation of ice crystallites during freezing of the suspension changes the material texture. Obtained results are of importance for deeper insight into the mechanism of the interfacial behavior of complex solutions under different confined space effects and due to the influence of organic co-solvents.     

Microdetermination of Molybdenum in Iron and Biological Samples by Adsorption Voltammetry

Abstract

Molybdenum has been determined by adsorption′voltammetry in a pH 2.40 buffer solution (0.005M N_aH₂PO₄-0.01M H₃PO₄). Utilizing the Strong adsorption of 12-molybdenum phosphate at a hanging mercury electrode, nanomole sensitivities are achieved. The derivative peak current is directly proportional to the concentration of molybdenum (VI) over the range of 5×10–9?2×10^?7M. The detection limit is 4×10^?9M.