Photocatalytic Degradation of Malachite Green using Undoped and Carbon-Doped Calcium Molybdate Catalysts

Calcium molybdates (undoped and carbon-doped) have been used as a photocatalyst for the degradation of malachite green. These have been characterized by different techniques such as FE-SEM, EDX and XRD. The progress of the reaction has been monitored spectrophotometrically. Different rate affecting parameters like pH, concentration of dye, amount of semiconductor and light intensity have been studied and their optimum values obtained are pH 9.7, concentration of malachite green as 5.00 × 10-4 M, 0.12 g of CaMoO4 and light intensity as 50.0 mWcm–2. A tentative mechanism for the photocatalytic degradation of dye has been proposed, where hydroxyl radical has been observed as an active oxidizing species.

Study of the kinetics of calcium molybdate leaching with sodium carbonate solutions

Calcium molybdate forms powellite, it is produced as a result of oxidizing roasting of off-grade molybdenum sulphide concentrates and other molybdenum materials with calcium additives (calcium oxides and hydro xides, calcium chlorides) in air at the temperatures of 550–600 oC. Use of Na2CO3 solutions enables an efficient recovery of Мо from CaMoO4 and a quantitative removal of impurities. To determine the optimum conditions for this process, one would need data on CaMoO4 leaching within a broad range of Na2CO3 concentrations and at high temperature and one would need to analyze the composition of the solid phase and the kinetic parameters of the process, i.e. rate and rate-controlling step. The authors look at the CaMoO4 leaching kinetics in 1.0–2.5 mol/l Na2CO3 solutions at 60–90 oC. It was found that the process rate is dictated by the stirring intensity and tends to increase with a rising temperature and the reagent concentration rising in the range of 1.0–1.5 mol/l. A higher concentration of Na2CO3 has no effect on the reaction rate. An apparent reaction order was determined in the Na2CO3 concentration range of 1.0–1.5 mol/l. An equation is proposed for calculating the CaMoO4 dissolution rate for the Na2CO3 solution and the temperature of 80 oC. It was established that a kinetic mode of leaching takes place in the soda concentration range of 1.0–1.5 mol/l amid intensive stirring. It is demonstrated that, within the studied Na2CO3 concentration range, calcite СаСО3 is formed after vaterite, a less stable phase of calcite, with crystallization of double sodium-calcium carbonates Na2Са(CO3)2·nH2O (n = 0, 2, 5) occurring at the same time. With the concentration of soda being >1.5 mol/l, the process is controlled by internal diffusion. In this region, the leaching rate is independent of the Na2CO3 concentration. Formation of double carbonates is associated with an additional consumption of soda. Therefore, when using this system one should consider how CaMoO4 typically dissolves in Na2CO3 solutions. The presence of these compounds in the soda solution after molybdenum leaching may impact the recovery of Мо from the solution using the known techniques. It may also hinder the recirculation of sodium carbonates going for the second leaching cycle.

OXIDATIVE ROASTING OF INDUSTRIAL SPENT CATALYSTS CO-Mo/Al2O3 HYDROPROCESSING WITH LIM

The oxidative roasting of industrial spent catalyst Co-Mo/Al2O3 for the hydrotreatment of diesel fuel with lime in an air atmosphere was studied. Using the data of DTA, TG and X-ray phase analysis, it was found that during roasting, the sulfur and carbon oxides forms CaSO4 and CaCO3, and Mo is converted to calcium molybdate. Using the filtering fixed bed of reagents, the kinetics of roasting was studied. It was found that in the temperature range of 550 – 600 °C with air, supply rate of 3 l/min the process ends in 38 - 44 min for ground and non-ground catalyst. The optimal parameters (lime consumption, temperature, and time of roasting) of the absorption of sulfur oxides during roasting were determined. The degree of sulfur and carbon oxides adsorption is 96 and 36%, respectively. Separation of roasting products using unmilled spent catalyst is proposed into a small fraction (contains a mixture of CaSO4, CaCO3 and CaO) and a coarse (consists of Al2O3, CaMoO4, CoO) fractions, and their separate processing. It has been shown that in the separate processing of roast fractions by a sodium carbonate solution, it is possible to separately obtain alumina (catalyst base) with cobalt oxide, a molybdenum-containing solution, and also a mixture of sulfate, carbonate and oxide calcium. The used method of roasting the spent hydrotreating catalyst with lime will allow hazardous waste of hazard class 3-4 to be disposed of without hazardous waste gas costs. It allows one to obtain, during further processing, molybdenum and cobalt compounds, as well as finely divided alumina.

STUDY OF PHASES IN CRYSTALLINE SENTENCES

The objective of the study was to study the phases in the crystalline sentence of calcium molybdate with sodium metafanadat on the basis of phase equilibrium in binary sentence. For this sutyd, different mixtures are prepared based on different molar ratios and investigation is made about these different mixture physical properties. Finally, the study also draw a phase balanced chart for the studied substances. For methodology adopted, nine samples were prepared. The results shows that to form a solid solution as dissolving sodium metafandate in calcium molybdate up to 40% of sodium metafanadate and form a solid solution in this sentence confirms that the necessary conditions to form a soid solution. It is concluded that for difference less than 15%, unlimited solid solution is formed; whereas, for difference above 15%, limited solid solution is formed. Our conclusion also shows that these two elements solubility is limited where one possesses the characteristic of high electronegativity, while, the other possess the characteristic of low electro negativity.

Novel CaMoO4@GO Nanocomposite: Synthesis, Characterization, and Investigation its Photocatalytic Properties

The current study aims to synthesize and characterize Calcium Molybdate-Graphene Oxide (CaMoO4@GO) nanocomposite under ultrasonic irradiation. Primarily, degradation of Methylene blue (MB) under Uv-Vis light was investigated to measure the photocatalytic properties of the as-synthesized CaMoO4@GO nanocomposite. In addition, various graphene oxide concentrations were applied to investigate its impact on the optical and photodegradation properties of calcium molybdate. X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectra energy dispersive analysis of X-ray (EDS) were used to characterize CaMoO4@GO nanocomposite. DRS results demonstrated that GO influenced significantly the optical properties of CaMoO4 as much as band gap of CaMoO4@GO nanocomposite shows a redshift in comparison with pure CaMoO4. Consequently, photocatalytic results demonstrated that adding GO causes to increase photodegradation of MB form 65% (CaMoO4) to 89% (CaMoO4@GO).

First results from the AMoRE-Pilot neutrinoless double beta decay experiment

The advanced molybdenum-based rare process experiment (AMoRE) aims to search for neutrinoless double beta decay ($$0\nu \beta \beta $$0νββ) of $$^{100}$$100Mo with $$\sim 100\,\hbox {kg}$$∼100kg of $$^{100}$$100Mo-enriched molybdenum embedded in cryogenic detectors with a dual heat and light readout. At the current, pilot stage of the AMoRE project we employ six calcium molybdate crystals with a total mass of 1.9 kg, produced from $$^{48}$$48Ca-depleted calcium and $$^{100}$$100Mo-enriched molybdenum ($$^{48{{\text {depl}}}}\hbox {Ca}^{100}\hbox {MoO}_{4}$$48deplCa100MoO4). The simultaneous detection of heat (phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot $$0\nu \beta \beta $$0νββ search with a 111 kg day live exposure of $$^{48{{\text {depl}}}}\hbox {Ca}^{100}\hbox {MoO}_{4}$$48deplCa100MoO4 crystals. No evidence for $$0\nu \beta \beta $$0νββ decay of $$^{100}$$100Mo is found, and a upper limit is set for the half-life of $$0\nu \beta \beta $$0νββ of $$^{100}$$100Mo of $$T^{0\nu }_{1/2} > 9.5\times 10^{22}~\hbox {years}$$T1/20ν>9.5×1022years at 90% C.L. This limit corresponds to an effective Majorana neutrino mass limit in the range $$\langle m_{\beta \beta }\rangle \le (1.2-2.1)\,\hbox {eV}$$⟨mββ⟩≤(1.2-2.1)eV.