Kinetic Study of Calcium Phosphate Precipitation in the System H3PO4-Ca(OH)2-H2O at 30°C

The precipitation kinetics of calcium phosphates, namely, hydroxyapatite (HAP), dicalcium phosphate dihydrate (DCPD), dicalcium phosphate anhydrous (DCPA), and monocalcium phosphate monohydrate (MCPM), were studied at 30°C by mixing calcium hydroxide, water, and phosphoric acid. The studied mixture was selected according to the stability domain of different calcium phosphates by referring to the phase diagram of the ternary system of H3PO4-Ca(OH)2-H2O at 30°C. The precipitation reaction has been monitored by following the changes in the conductivity, pH, and calcium concentration. The solid phases formed at different stages of this precipitation were characterized by X-ray diffraction.

Technological studies of the use of modifiers in the flotation of calcium-containing minerals

Using samples of skarn scheelite-sulfide ore from the Vostok-2 deposit, studies were carried out to model combinations of increased dose of inorganic modifiers (sodium carbonate, water glass, sodium sulfide) based on publications by foreign researchers on the achieved positive result in increasing the contrast of the mineral surfaces of scheelite and calcite and their floatability. Testing was carried out according to the standard flowsheet on tap and recycled water. Oxyhydryl collector was sodium oleate of technical acid B-115, dose 250 + 50 g/t. The order of feeding modifiers (sequential supply and combination of a mixture of sodium carbonate (bicarbonate) + water glass), the effect of the temperature of the pulp upon contact, the dose of modifiers and the ratio of components in the mixture were studied. The dose of water glass varied from 350 to 1450 g/t, sodium carbonate (bicarbonate) varied from 0 to 11.5 kg/t, sodium sulfide up to 4.9 kg / t. With increased dose of inorganic modifiers, it was not possible to achieve selective depression of calcite and apatite while maintaining effective scheelite flotation. The use of sodium bicarbonate in comparison with sodium carbonate, at the same flow rates, creates a less alkaline pH in the flotation pulp, which leads to an increase in the concentration of hardness ions [Са2+, Mg2+] and overdose of the collector. Using combinations of reagents: sodium carbonate (bicarbonate) + water glass, sodium sulfide + sodium hydroxide + water glass, even with a slight increase in the dose of water glass in the mixture, after heat treatment, concentrates of lower quality were obtained, with increased losses of scheelite compared to the factory mode according to the Petrov method.

Effect of cavity-cleaning agents on shear bond strength between self-etching adhesives and dentin

Aim: The effect of cavity-cleaning agents on shear bonding strength between self-etching adhesives and dentin was evaluated. Methods: Twenty-five healthy human third molars were worn to obtain flat middle dentin. The samples were randomly divided into five groups according to the cleaning agent used: group CB not treated with any cavity disinfectants and served as control. Following groups, dentin surfaces were treated with 2% chlorhexidine (CHX group); 3% hydrogen peroxide (HP group); calcium hydroxide water (CH group); and 70% ethyl ethanol (E group). The dentin surfaces were cleaned by friction for 20 s and dentine bonding agent, Clearfil SE Bond, was applied. Cylinders (5.0 mm  1.2 mm, n = 19) of fluid composite resin were placed on the dentin surface, and the teeth were stored in deionized water at 37°C for 24 h. Subsequently, the samples were subjected to the shear bonding test, and the obtained values were subjected to one-way ANOVA and Tukey’s test (α = 0.05). The failure pattern was analyzed descriptively by examining the specimens with a stereoscope at a magnification of 4, and failure was classified into adhesive, cohesive or mixed type. Results: Shear bonding was significantly lower in group HP (6.17 ± 5.69 MPa). The groups CB, CHX, CH and E were statiscally similar, 22.15 ± 6.54MPa; 18.40 ± 7.26MPa; 18.07 ± 5.98MPa ; 16.43 ± 6.19MPa respectively. The failure modes observed were only adhesive and mixed. Conclusion: The use of 2% chlorhexidine, calcium hydroxide water, and 70% ethyl ethanol did not negatively affect bond strength. Only 3% hydrogen peroxide is contraindicated as a cavity cleaner in adhesive restorative procedures when self-etching system is used.

Thermodynamic evaluation using the law of mass action under consideration of the activity coefficients in the system NdCl3-HCl (or NaOH)-H2O-DEHPA-kerosene

For the recovery of neodymium, an important rare earth metal, solvent extraction using DEHPA as extractant is a possible process for winning and recycling. A preceding study by the authors has provided extensive experimental data of the system neodymium-chloride-hydrochloric acid (or sodium hydroxide)-water-di-(2-ethylhexyl)phosphoric acid (DEHPA)-kerosene. It was found that the description of the reaction Nd3++3(DEHPA)2 ⇄ Nd(DEHP‧DEHPA)3+3H+ by an ideal mass action law is only partly satisfactory. This article investigates the contribution of several parameters to non-ideality. On this basis, expressions for activity coefficients of neodymium in the aqueous phase as well as DEHPA and neodymium in the organic phase are derived. The resulting equations are shown to represent the system with considerably better accuracy than previously possible.