Adsorption Of Hydroxamate Research Articles

Studies on the nature of salicyl hydroxamate adsorption at the surface of neodymium oxide

Adsorption of salicyl hydroxamic acid (SHA) on neodymium oxide (Nd2O3) surfaces was studied at different SHA concentrations. The adsorbed surfaces were examined using X-Ray Diffraction (XRD) and Laser Raman Spectroscopy (LRS). XRD results show that the oxide remains intact until stoichiometric amounts equivalent to Nd(SHA)3 were exceeded. At lower concentrations, the behavior appeared to be an ion exchange of SHA with hydroxide as well as carbonates and chlorides. Results are attributed to a monolayer of chemisorbed SHA at low concentrations and multilayers of surface precipitated Nd(SHA)3 at higher concentrations. LRS corroborated these findings. Peaks from the C-H stretching band and C = N vibration bands were identified and areas under the peaks were quantified. Formation of the hydroxamate compound was ascertained from the C = N bands around 1597 cm−1. It was concluded that chelation occurs through chemical bonding of SHA with surface Nd confirming chemisorption and with trivalent Nd confirming surface precipitation. Thermodynamic calculations in the form of solubility speciation diagrams suggest that chemisorption predominates at moderate pH between 6 and 9 and surface precipitation predominates at higher pH between 9 and 12. Adsorption isotherms were determined for the monolayer and found to yield free energy values between physisorption and chemisorption but, due to the reaction being ion exchange, it was concluded to be chemisorption.

Alternative flowsheet for rare earth beneficiation of Bear Lodge ore

The Bear Lodge Project is an important rare earth deposit in the United States. While extensive previous studies have settled on a crushing, screening, gravity and magnetic separation process, this study sets out to investigate an alternative flowsheet based on flotation and wet high intensity magnetic separation (WHIMS) to effectively beneficiate the rare earth oxide (REO) content of the Bear Lodge ore. Mineral characterization found ancylite was the dominant rare earth mineral, associated mainly with calcite and strontianite. Electrokinetic studies on the effects of pH, concentrations of various ions (Sr2+, HCO3− and CO32−) and hydroxamate concentrations were performed to establish the electric nature of the Bear Lodge ore. The isoelectric points (I.E.P) of the material in distilled water was around 5.27. The Sr2+ and CO32− ions in solution significantly affected the surface charge of the material. Adsorption studies suggested that the mechanism of hydroxamate adsorption is chemisorption, as hydroxamate adsorption increased on the Bear Lodge ore with an increase in temperature. WHIMS was employed to remove the iron content to reduce the interference of iron in following flotation process and consumption of hydroxamic acid. After cleaner flotation a REO grade of 11.2% at 72.7% recovery from a feed material of 4.5% REO was obtained. In light of the loss of REO in WHIMS process, it is possible to produce a concentrate containing 11.2% REO grade at 61.2% recovery.

A model system for the investigation of rare earth collector interaction

A model system was used to investigate the interaction between carbonate mineral and octanohydroxamate collector. Bastnaesite (Ce) is the most important rare earth mineral that has been the dominant the rare earth source since 1960s. In this study, a synthetic cerium carbonate thin film on a calcite (most common gangue mineral occurring with rare earth minerals) substrate was formed for a surface interaction investigation. The cerium carbonate thin film system was characterized using Raman spectroscopy, atomic force microscopy and magnetic atomic force microscopy. An adsorption study between the model compound and hydroxamate was also conducted. The study established the utility of using atomic force microscopy and magnetic atomic force microscopy to investigate the mineral surface interaction. Weak adsorption on the thin film surface was observed after 5h and 24h of conditioning and the hydroxamate adsorption became evident after 72h of conditioning. The adsorption studies for cerium carbonate and calcite also demonstrated that hydroxamate is selective to Ce over Ca.

Fundamentals of rare-earth flotation surface chemistry: Hydroxamate adsorption on bastnasite

Fundamentals of rare-earth flotation surface chemistry: Hydroxamate adsorption on bastnasite

Surface chemistry aspects of bastnaesite flotation with octyl hydroxamate

Surface chemistry features of bastnaesite were investigated with respect to octyl hydroxamate adsorption and the wetting characteristics at different levels of hydroxamate adsorption. The wetting characteristics of bastnaesite in the absence of collector adsorption were examined using both contact angle measurements and MD simulations. As expected, it was found that bastnaesite is naturally hydrophilic. Surface chemistry studies included octyl hydroxamate adsorption by the solution depletion method. The surface state was described by sum-frequency vibrational spectroscopy (SFVS) and molecular dynamic simulations (MDS). The adsorption isotherm at low levels of hydroxamate adsorption was established and the hydrophobic surface state was described from contact angle measurements. The relationship between hydrophobicity and adsorption density was examined for the first time by MD simulations. The SFVS spectra indicate that a well-ordered monolayer was formed at a hydroxamate concentration of about 1×10−4M.

モナズ石に対するオクチルヒドロキサム酸塩の吸着

Adsorption isotherms of octylhydroxamate and the relationship between octylhydroxamate adsorbed and phosphate released have beenmeasured against monazite. These results have been compared to those against synthetic CePO4and LaPO4. Adsorption of hydroxamate on monazite takes as long as several daysto reach equilibrium. The maximum adsorption of hydroxamate on monazite occurs at pHabout 10. Hydroxamate adsorption on monazite is much higher thanon CePO4or LaPO4and forms multilayer. Monolayer adsorption ofhydroxamate on monazite is mainly due to substitution reaction with lattice phosphate ions and makes surface hydrophobic. On the other hand, multilayer adsorption may be caused by precipitationof rare-earth metal hydroxamates and other mechanisms, such as hydrophobic bonding or hydrogen bonding between hydroxamate molecules. Hydroxamate adsorption is enhanced at elevated temperature, but flotation recoveryis not. This may be explained by a reason that the increase oftemperature promotes multilayer adsorption of hydroxamate which donot contribute to surface hydrophobicity.

An electrochemical investigation of the adsorption of octyl hydroxamate on chalcocite

The electrochemical aspects of octyl hydroxamate adsorption on chalcocite were investigated through linear potential sweep voltammetry, contact angle measurements, and flotation tests in a polarizable Hallimond tube. The adsorption of octyl hydroxamate was found to coincide with an oxidation shoulder, just prior to the primary anodic peak. The electrode reaction associated with this peak has been explained as an oxidation/complexation/adsorption process which accounts for the interaction between octyl hydroxamate and chalcocite.

Adsorption of hydroxamate collectors on semi-soluble minerals part II: Effect of temperature on adsorption

The effect of temperature on the adsorption of potassium octyl hydroxamate on barite, calcite, and bastnaesite has been investigated. The results of this adsorption study at elevated temperatures exhibit increased uptake of potassium octyl hydroxamate with temperature on barite, calcite, and bastnaesite minerals, suggesting endothermic chemisorption mechanism with large entropic effects. The large entropies can be attributed to the relative loosening of ordered water structures at the mineral surface and in the bulk during the adsorption process and are also due to hydrophobic chain association effects. The effect of temperature on adsorption is relatively more pronounced in the case of bastnaesite than in the case of the two other minerals, namely barite and calcite.

Adsorption of hydroxamate collectors on semisoluble minerals Part II: Effect of temperature on adsorption

The effect of temperature on the adsorption of potassium octyl hydroxamate on barite, calcite, and bastnaesite has been investigated. The results of this adsorption study at elevated temperatures exhibit increased uptake of potassium octyl hydroxamate with temperature on barite, calcite, and bastnaesite minerals, suggesting endothermic chemisorption mechanism with large entropic effects. The large entropies can be attributed to the relative loosening of ordered water structures at the mineral surface and in the bulk during the adsorption process and are also due to hydrophobic chain association effects. The effect of temperature on adsorption is relatively more pronounced in the case of bastnaesite than in the case of the two other minerals, namely barite and calcite.

The adsorption of hydroxamate on semi-soluble minerals. Part I: Adsorption on barite, Calcite and Bastnaesite

The uptake of potassium octyl hydroxamate on barite, calcite and bastnaesite has been determined as a function of time, reagent concentration and pH. The results of this adsorption study indicate a surface reaction/chemisorption mechanism whereby the cations on the mineral surface form hydroxy complexes in solution, readsorb at the interface, and then interact with the hydroxamate. The hydroxamate polar group is highly specific to rare-earth cations as compared to alkaline-earth cations, Ca ++ and Ba ++, giving rise to very extensive and rapid uptake on bastnaesite in comparison to calcite and barite. Multilayers of adsorbed hydroxamate form on bastnaesite and calcite.