Aqueous Suspension Of Calcium Hydroxide Research Articles

Research of textural and structural features of refractory gold-bearing ores

The article studies the material and mineralogical composition of the refractory gold-bearing ores of the weathering crust of one of the deposits in Eastern Siberia. It is revealed that, according to the textural and structural features, ores are multi-mineral and have significant differences in the composition of the detrital, granular material and the loose component. All ore is saturated with iron hydroxides and limonite crusts with clay components. The results of the analysis showed that large classes contain an insignificant amount of a valuable component. Increased gold content is noted starting from -4 + 0 mm size. In the free state are about 3-5%. Processing of these types of raw materials is a rather complicated task. Analysis of the enrichment methods showed that the use of new solvents of noble metals with their subsequent concentration is promising. Of practical interest are alkaline solutions obtained by dissolving sulfur in an aqueous suspension of calcium hydroxide. The reagent is non-toxic and environmentally friendly. Leaching was carried out in a wide range of concentrations of the solvent used. The optimum solvent concentrations and the duration of the leaching process for extracting the valuable component into the filtrate were determined to be 97–98%. Chemical analysis of cakes showed that the reagent does not enter into chemical interaction with other elements that make up the ore. As well as the content of elemental sulfur in dump cakes averages 0.64%, that is, it corresponds to a content in the raw material of up to 0.8%. At the same time, cakes are not environmentally harmful and can be stored on special platforms.

Efficacy of different irrigation techniques on calcium hydroxide removal from the root canal

Summary Introduction Calcium hydroxide (CH) is a medicament widely used in endodontic treatment due to its antibacterial, regenerative and biocompatible properties. Studies have shown that remaining CH on root canal walls and dentinal tubules can compromise sealer penetration, leading to its weak adhesion, volume change and, consequently, apical leakage. The aim of this study was to compare the efficacy of four different techniques in removing calcium hydroxide from the root canal. Material and Methods 32 extracted single-rooted teeth with one canal were used in this study. The canals were prepared using BioRaCe system (FKG Dentaire, Swiss) BR5 40/.04 with sodium hypochlorite irrigation after each instrument. Longitudinal grooves were formed on the proximal root surfaces. All canals (except negative control) were filled with aqueous CH suspension. After seven days of incubation, the teeth were allocated into the four groups (n=7), plus positive and negative control. Four techniques (systems) for CH removal were tested: conventional syringe irrigation (CSI), passive ultrasonic irrigation (PUI), XP-endo Finisher (FKG Dentaire, Swiss) and Canal Brush (Roeko, Coltene) with irrigation of 5 ml 2% NaOCl and 5 ml 10% citric acid. All the roots were then split into the two halves with chisel and observed under the stereomicroscope (Boeco, Germany) at magnification of 20x. The area with remaining CH on the root canal wall surface was then divided with the total root canal surface area (%). The obtained results were statistically processed using One-way ANOVA and Tukey post-hoc test (p<0.05). Results The most efficient system was XP-endo Finisher with 91.33% of clean surface, followed by PUI 88.36%, Canal Brush 87.83%, and CSI with 66.92%. Conclusion None of the systems completely removed the traces of the medicament from the root canal. For optimal clinical success, it is necessary to combine various systems with copious irrigation.

Properties of iron-containing nanohydroxyapatite-based composites

The paramagnetic properties of compounds resulting from the synthesis of nanohydroxyapatite in the presence of Fe(III) ions have been studied by electron paramagnetic resonance, Mossbauer spectroscopy, and magnetochemistry. Based on the obtained results on the mechanism of the reaction between an orthophosphoric acid solution and an aqueous calcium hydroxide suspension, we have found conditions for incorporating Fe(III) impurity ions into hydroxyapatite. We have studied samples differing in the sequence in which reagents were mixed and in hydroxyapatite crystallite formation conditions. It has been shown that, in all instances, the composition and properties of the iron-containing phases in the composites depend significantly on both synthesis and heat treatment conditions.

Larvicidal activity of micronized aqueous suspension of calcium hydroxide against Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

In the search of alternatives for the control of mosquitoes of medical importance, we evaluated the larvicidal activity of micronized suspensions of calcium hydroxide [Ca(OH)₂] against Aedes aegypti and Culex quinquefasciatus. Tests conducted under laboratory conditions determined a LC50 = 0.027% (LC90 = 0.096%) for A. aegypti and a LC50 = 0.092% (LC90 = 0.2%) for C. quinquefasciatus, at 24 h post-treatment. Considering that the LC50 for the less susceptible species killed 100% of larvae for both species at 48 h post-treatment, we decided to use the diagnostic concentration of 0.1% which eliminated 100% of larvae at 48 h under a simulated field trial. There was a residual effect for up to 84 and 70 days for A. aegypti and C. quinquefasciatus, respectively. Evaluation of Ca(OH)₂ on breeding sites showed a larvicidal activity of 100% for up to 56 days. When the micronized Ca(OH)₂ was incorporated at concentrations from 0.02% (w/v), a superficial film was formed which killed 100% of the larvae of both species after 24 h of contact, and the activity remains until the film broke apart due to stirring. The fact that Ca(OH)₂ is cheap and the people in rural areas of Mexico and other countries know the handling procedures for this compound led us to consider that 0.1% suspensions of Ca(OH)₂ could be used for mosquito control in deposits of water placed in human premises both in urban and rural areas.

Calcium release and pH‐characteristics of calcium hydroxide plus points

To evaluate calcium ion release and pH-characteristics of calcium hydroxide plus points (CHPP), conventional calcium hydroxide points (CHP, both Coltène/Whaledent, Langenau, Germany) and aqueous calcium hydroxide suspension (CHS) (Calxyl, OCO, Dirmstein, Germany). Ten CHPP or CHP of size 50 were immersed into 5 mL isotonic sodium chloride solution. Conventional Ca(OH)2-free gutta-percha points served as negative control. Calcium release was measured up to 44 days by means of complexometric titration. Time dependent pH behaviour of all points in comparison with CHS was determined immersing 30 points of size 50 into 2.3 mL 0.9% wt NaCl-solution at time intervals of 0.5-72 h by a microelectrode measuring chain and a pH-meter. The surface morphologies of new and used gutta-percha points were evaluated qualitatively under a scanning electron microscope. Statistical evaluation was carried out using Kolmogorov-Smirnov-tests, Mann-Whitney-tests and multifactorial anova. For CHPP, a threefold greater calcium release was measured compared with CHP. Both types of points as well as CHS showed a maximum pH of approximately 12. Differences between groups were statistically significant for calcium release and pH (multifactorial anova; P < 0.001). Both types of points showed porous surfaces after usage, with a rougher surface for CHPP. CHPP and CHP increased the pH of isotonic sodium chloride >11 within 3 min. CHPP had a greater release of Ca2+ compared with CHP.

Reaction of Calcium Hydroxide with the Oxide-Sulfate Fraction of Lead Battery Scrap

The reaction of oxide-sulfate fraction of lead battery scrap with an aqueous suspension of calcium hydroxide was studied experimentally.

Wet‐dry process of HCL removal from flue gas: experimental study on operating parameters

Wet‐dry process of hydrogen chloride removal from flue gas has been studied at pilot scale. Hot gas produced by methane burner, added with gaseous hydrogen chloride, is contacted by an aqueous suspension of calcium hydroxide in a cylindrical steel vessel 0.25 m I.D. and 4 m high. The effects of feed ratio Ca(OH)2/HCl, hydrogen chloride concentration in the inlet gas, operating temperature and residence time on the amount of hydrogen chloride removed have been exstensively investigated. The effect of inside wall fouling by Ca(OH)2 has also been evaluated. The experimental results show that the overall amount of hydrogen chloride removed increases when the feed ratio and the gas inlet concentration are increased and the operating temperature is decreased. However, the HCL removal does not seem affected by the residence time within the short interval investigated.

Influence of Surface Modifiers on the Structure of Precipitated Calcium Carbonate

A calcium carbonate (CaCO3) sorbent synthesized in the presence of surface modifiers has recently been developed in this laboratory for the purpose of enhancing the reactivity toward SO2 at high temperatures (800−1150 °C). The calcium carbonate particles are produced by precipitation from an aqueous suspension of calcium hydroxide by bubbling pure CO2. The operating parameters such as suspension concentration, gas flow rate, and concentration of surface modifiers are varied to study their influence on the particle size, surface area, and pore volume. The synthesized CaCO3 particles exhibit dramatically high SO2 reactivity and sorbent utilization. The increased reactivity is primarily due to the development of an open initial pore structure of the sorbent brought about by the action of surface-active agents, compared to the conventional calcium-based sorbents. ζ-potential measurements indicate that addition and subsequent adsorption of anionic surfactants neutralize the high positive surface charge (30 mV)...

High Surface Area Calcium Carbonate: Pore Structural Properties and Sulfation Characteristics

Limestone or calcium carbonate (CaCO3) used as a sorbent in the removal of acid gas precursors (SO2) from combustion systems suffers from poor pore structural properties which causes low reactivity and incomplete utilization. The surface area and pore size distribution of CaCO3, if tailored appropriately, can considerably enhance its reactivity for SO2. This study focuses on the optimization of pore properties of CaCO3 particles and the enhancement of SO2 reactivity and ultimate utilization. The carbonate is produced by precipitation from an aqueous suspension of calcium hydroxide by injecting CO2. The influence of operating parameters, suspension concentration, gas flow rate, and additives (surfactant) on the surface area and pore volume is investigated. The surface area of the carbonate powder can be controlled in the range of 10−70 m2/g by varying the operating parameters. The SO2 reactivity and the ultimate utilization of the calcium carbonate indicate a dramatic improvement and can be correlated with...

Effect of root canal filling materials containing calcium hydroxide on the alkalinity of root dentin.

The effect of root canal filling pastes containing calcium oxide resp. calcium hydroxide on the alkalinity of extracted human teeth was investigated using a colour indicator (cresol red). An aqueous suspension of calcium hydroxide (Pulpdent), which is normally used for temporary root canal filling, most consistently produced alkalinity. Removal of the smear layer following instrumentation of the root canal led to increased proportion of alkaline-positive spots in dentinal locations distant from the canal. A clearly smaller effect was found with a calcium salicylate cement (Sealapex) and an oil-paste (Gangraena Merz), both of which are available for definite root canal fillings. Following removal of the smear layer, these hard-setting preparations caused moderate alkalinity in dentin adjacent to the canal but no effect was observed in locations more distant from the canal. Neither at locations adjacent to nor distant from the root canal was alkalinity found when another calcium salicylate cement (Apexit) was used. Apparently the release of hydroxyl ions into root dentin from calcium hydroxide containing root canal filling materials is not solely influenced by the absolute amount of calcium hydroxide, but also depends on other ingredients which variably inhibit the release of these ions.

Precipitation mechanism of calcium carbonate fine particles in a three-phase reactor

Calcium carbonate (CaCO 3) particles are produced from precipitate in an aqueous suspension of calcium hydroxide (Ca(OH) 2) by injecting CO 2 gas. Three types of calcite particles, i.e. rhombohedral, rounded and slender particles, were finally obtained by changing the operating conditions, though in the early stage of the reaction amorphous calcium carbonate is always formed. The relationship between the particle shape or size and the operating conditions is investigated, and the mechanism of formation of these types of particles is discussed.