Calcium Hydroxide Research Articles

Irrigation techniques for calcium hydroxide removal from resorption cavities

Irrigation techniques for calcium hydroxide removal from resorption cavities

Lipoteichoic Acid from Lacticaseibacillus rhamnosus GG as a Novel Intracanal Medicament Targeting Enterococcus faecalis Biofilm Formation.

The demand for safe and effective endodontic medicaments to control Enterococcus faecalis biofilms, a contributor to apical periodontitis, is increasing. Recently, lipoteichoic acid (LTA) of family Lactobacillaceae has been shown to have anti-biofilm effects against various oral pathogens. Preliminary experiments showed that LTA purified from Lacticaseibacillus rhamnosus GG (Lgg.LTA) was the most effective against E. faecalis biofilms among LTAs from three Lactobacillaceae including L. rhamnosus GG, Lacticaseibacillus casei, and Lactobacillus acidophilus. Therefore, in this study, we investigated the potential of Lgg.LTA as an intracanal medicament in human root canals infected with E. faecalis. Twenty eight dentinal cylinders were prepared from extracted human teeth, where two-week-old E. faecalis biofilms were formed followed by intracanal treatment with sterile distilled water (SDW), N-2 methyl pyrrolidone (NMP), calcium hydroxide (CH), or Lgg.LTA. Bacteria and biofilms that formed in the root canals were analyzed by scanning electron microscopy and confocal laser scanning microscopy. The remaining E. faecalis cells in the root canals after intracanal medicament treatment were enumerated by culturing and counting. When applied to intracanal biofilms, Lgg.LTA effectively inhibited E. faecalis biofilm formation as much as CH, while SDW and NMP had little effect. Furthermore, Lgg.LTA reduced both live and dead bacteria within the dentinal tubules, indicating the possibility of minimal re-infection in the root canals. Collectively, intracanal application of Lgg.LTA effectively inhibited E. faecalis biofilm formation, implying that Lgg.LTA can be used as a novel endodontic medicament.

Comparison of Modified NeoPutty MTA®, Biodentine, and Calcium Hydroxide in Indirect Pulp Therapy in Deciduous Teeth: An In Vivo Clinical Study

Comparison of Modified NeoPutty MTA®, Biodentine, and Calcium Hydroxide in Indirect Pulp Therapy in Deciduous Teeth: An In Vivo Clinical Study

Study on Synthesis of CSH Gel and Its Immobilization of Heavy Metals

Calcium silicate hydrate (CSH) gel is the most important hydration product of cement. It influences the mechanical properties of resulting materials and plays an important role in the adsorption and immobilization of heavy metal ions. Research in the structure of CSH gel and its ability for heavy metal immobilization enables the development of tailored cement-based materials, a feature that holds significant future potential. In this study, CSH gel was synthesized under different pH and Ca/Si conditions. Structural and morphological changes in CSH gel were investigated using modern technologies. The results revealed that both pH and Ca/Si ratios were important factors influencing the structure of CSH gel. During the formation of CSH, both Cr3+ and Pb2+ can be incorporated into CSH gel, and promoting the formation of calcium hydroxide Cr3+ can also replace Si4+ in the Si-O bond.

DEVELOPMENT OF DRY BUILDING MIXTURES BASED ON REDISPERSIBLE POWDER FOR REGULATING THE PROPERTIES OF PLASTER MIXTURES

The relevance of the work. The results is theoretically substantiated and experimentally confirmed the possibility of obtaining a dry additive-retarder of gypsum setting based on lime and polyvinyl acetate dispersions due to the formation of polyvinyl alcohol and salts of calcium acetate in the result of alkaline hydrolysis of polyvinyl acetate dispersion (PVAD) with the slaked lime in hydrated lime. The results of the work implemented in the production of dry gypsum mixes. Purpose. The development of dry building mixes based on gypsum and time increase of time of their conformance through adding of complex additives on the basis of burnt lime and polyvinyl acetate dispersions [PVAD]. Methodology. The study used standard research techniques to determine physical and mechanical properties of gypsum binders and quality of complex additives according to ДСТУ Б В.2.7-82:2010, ДСТУ Б В.2.7-23-95, ДСТУ Б В.2.7-171:2008. Study of phase composition of materials, micro – and macrostructure was carried out by x-ray diffraction, electron and light microscopy. The results. The influence of the main components of the additive (polyvinyl acetate dispersion and lime) on the properties of hemihydrate gypsum is investigated. The chemistry of the interaction of components of the complex additive, according to which the result of alkaline hydrolysis of polyvinyl acetate is formed: polyvinyl alcohol, a feature of its molecules structure is the presence of hydrophilic OH−groups and the hydrophobic component − a hydrocarbon radical. The hydrophilic part of the molecule being ion adsorbed on the surface of the particles of the binder, forms a monomolecular layer that is oriented with the hydrophobic part of the gypsum particles. It is also possible the formation of calcium acetate Ca(СН3СОО)2, which increases the concentration of calcium ions in solution. The combined effect of hydrolysis products significantly reduce the solubility of hemihydrate, the rate of formation of crystallization centers, due to the slowing effect of these supplements.

Evaluating Alkali Activation in Magnesium Slag Carbonization and Its Mechanism

In recent years, magnesium slag has been used as a raw material for solid waste treatment using the carbonization method and has proven to be promising in reducing carbon emissions. In this study, the alkali activation reaction was introduced to promote the carbonization of magnesium slag. The resulting mechanical properties, microstructural attributes, and carbonization mechanism were studied by varying the sodium hydroxide content, temperature, and carbon dioxide concentration during the reaction process. The results showed that the amounts of calcium hydroxide, C-S-H, and calcium carbonate in the reaction products increased with the sodium hydroxide content, which enhanced the compressive strength of the composite. However, it does not influence the carbonization mechanism with the increasing reaction temperature, which only elevates the reaction rate. With the increase in the carbon dioxide concentration during alkali activation, the carbonization reaction is dominated by the amount of CO2 dissolved in the reaction medium, and the carbonization mechanism is changed. Thus, a significant decrease in the calcium hydroxide content and a sharp increase in the calcium carbonate content in the products occurred, which significantly improved the compressive strength of the resulting magnesium slag composite. Among them, the maximum compressive strength is 6.83 MPa.

Bio-based coatings containing mycosporine-like amino acids (MAA) to control sunscald abiotic stress in orange fruit (Citrus sinensis L)

Oranges are susceptible to many abiotic stresses, and the fruit is particularly susceptible to sunscald, a physiological disorder caused by excessive solar radiation. Sunscald is commonly controlled by spraying the fruits with calcium hydroxide and/or kaolin, but this procedure is not always effective due to rain and the application of phytosanitary treatments. Since mycosporine-like amino acids (MAAs), produced by many marine organisms, protect them against ultraviolet radiation UV-A and UV-B, these compounds could be incorporated into bio-based emulsions to control sunscald in oranges. Therefore, increasing concentrations of the commercial product Helioguard™ 365 (0 %, 1 %, 2 %, and 4 % - v/v), a source of MAAs, were incorporated into lipid-based emulsions. The emulsions were applied during the final stage of development of ‘Hamlin’, ‘Pera-rio’, and ‘Valencia’ oranges at 21-day intervals. Spraying with 5 % (w/v) calcium hydroxide served as the positive control treatment, while untreated fruits served as the negative control. Incorporating MAA into the emulsion did not demonstrate effective control of sunburn compared to the positive control treatment with calcium hydroxide, as all fruits exhibited varying degrees of sunscald, ranging from low to high severity. Regarding physicochemical parameters, as well as oxidative metabolism, except for color parameters, soluble solids content, ascorbic acid, and overall biochemical parameters, there was no difference among treatments for any of the evaluated orange cultivars. The activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) did not show consistent with efficient antioxidant potential capable of significantly reducing the malondialdehyde (MDA) content. Despite using MAA at the evaluated concentrations and experiencing severe climatic interference in 2020, efficient control of sunscald in oranges was not achieved. Further research is needed to identify more effective alternatives and gain a better understanding of how climate affects oxidative aspects.

Early hydration and mechanical performance of composited cementitious system prepared from high temperature calcined molybdenum tailings

To improve the recycling of solid waste and achieve the secondary utilization of waste resources, this study investigates the preparation of molybdenum tailings composited binders by high temperature calcination using molybdenum tailings, limestone, bauxite, and iron concentrate powder. Besides, to explore the mechanical properties of the new molybdenum tailings composited binders, a molybdenum tailings composited mortar was prepared. The mechanical properties, micro performance and hydration mechanism of the new molybdenum tailings composited binders were studied. Finally, the carbon dioxide emission of green molybdenum tailings composited binders/molybdenum tailings composited mortar was evaluated by the life cycle assessment method. The results show that the compressive strength of molybdenum tailings composited binders gradually increases with the increase of calcination temperature. When the calcination temperature is 1350 °C, the compressive strength and flexural strength at 28 days are 44.17 MPa and 7.56 MPa, respectively, which are 3.65 % and 4.63 % higher than control group made by P·O 42.5 cement. The early strength of molybdenum tailings composited binders increases slowly, and the later strength increases rapidly. In addition, there is more C2S in the matrix, resulting in a slow hydration heat rate and low cumulative hydration heat. Compared with other groups, the hydration kinetic parameters and hydration rate of molybdenum tailings composited binders under 1350 °C were the lowest. The main hydration prodcuts of molybdenum tailings composited binders are C-S-H, calcium hydroxide, and Aft gels. Compared with P·O 42.5 cement paste and mortar, the carbon dioxide emission of molybdenum tailings composited binders/molybdenum tailings composited mortar is reduced by 42.82 % and 29.08 %, respectively, which can indicate that the new binders can produce less carbon dioxide. Overall, this study can provide new ways for the development of the new binder mixed with plenty of molybdenum tailings, and offer a novel way for recycling the molybdenum tailings, and also present some valuable experimental results for the application of molybdenum tailings in infrastructures.

Lime Stabilization of Tropical Soil for Resilient Pavements: Mechanical, Microscopic, and Mineralogical Characteristics.

Lime stabilization is a sustainable technique due to its use of local materials, increased durability, reduced maintenance, and improved resistance to water action. This paper examines the impact of lime stabilization on the mechanical, microscopic, and mineralogical properties of a tropical soil. Two types of lime, calcitic and dolomitic, were tested at 3% and 5% by weight. Compressive, indirect tensile and flexural test results and statistical analysis revealed that calcitic lime mixtures had higher strength and stiffness, whereas dolomitic lime mixtures exhibited greater deformability with higher tensile strain at break. Scanning electron microscopy indicated that the soil's porous matrix closed within 7 days for both lime types due to flocculation, with increased matrix interlocking over time. The calcitic lime mixture developed a more closed matrix compared to the dolomitic lime, which showed weaker cementing. X-ray diffraction analysis indicated higher consumption of clay minerals and a notable reduction in calcium hydroxide peaks in the lime-treated soils. The study concludes that calcitic lime provides better pavement performance for stabilizing the soil, enhancing its engineering properties while also being sustainable by reducing the need for raw material extraction and improving resilience to climate-related issues such as floods.

Formulation and characterization of one-part Ca-based alkali-activated slag-steel slag materials

This study aims to develop one-part Ca-based alkali-activated materials (OCAM) using steel slag (SS) and slag powder (SP) with a Ca-based activator. The effects of SS replacement rate on the flowability, setting time, and mechanical properties of paste were systematically investigated. Furthermore, methods such as Mercury intrusion porosimetry (MIP), heat of hydration, X-ray diffraction (XRD), and scanning electron microscope (SEM) were used to compare the effects of calcium oxide (CO) and calcium hydroxide (CH) on the microstructure of the OCAM. The results indicate that the addition of SS enhances mortar flowability and setting time, with optimal mechanical properties when the SS replacement rate is 20 %. However, strength gradually decreases as the replacement rate increases beyond this point. In addition, the incorporation of CO further enhances the mechanical properties of mortar. MIP test results show that the use of CO reduces the internal porosity and refines the micropore structure, although it also increases drying shrinkage. The hydration heat test results reveal that the use of CO increased the total heat release of the sample in the initial 72 h and accelerated the early hydration reaction. Moreover, XRD and SEM results indicate that CO improves carbonation resistance.

The Efficacy of Aloe vera Against Enterococcus faecalis as an Intracanal Medicament: A Systematic Review and Meta-Analysis.

Calcium hydroxide (CaOH) is commonly used as an intracanal medicament due to its antimicrobial properties; its antibacterial property depends on the release of hydroxyl ions. By analyzing experimental in vitro studies related to the research question, many studies carried out bacterial inoculation on extracted human teeth or laboratory Petri dishes.This review article seeks to assess the antimicrobial efficacy of Aloe vera (AV) againstEnterococcus faecalisin comparison to CaOH as an intracanal medicament.After being retrieved from databases such as PubMed, Scopus, the Cochrane Library, and EBSCOhost, publications from 2013 to 2024 were screened against our inclusion criteria. As a result, seven papers were included in the systematic review and four in the meta-analysis. Using a meta-analysis (Stata software version 16.0, StataCorp LLC, College Station, TX) to compare colony-forming units (CFUs) formed by CaOHand AV, forest plots were created to record the specimen size, mean, and standard deviation value of the outcome in CFU, at 95% confidence intervals. AV exhibits bactericidal qualities that are equal to or comparable to those of CaOH. AV displayed a nonsignificantly reduced CFU count than CaOH in a meta-analysis (p > 0.05). In summary, AV exhibits antibacterial/antimicrobial capabilities against E. faecalis that are equal to or comparable to CaOH.

Effectiveness of mechanical vs. chemomechanical methods in removing intracanal calcium hydroxide medication: a randomised trial.

To compare the mechanical and chemomechanical methods for removing calcium hydroxide medication from the root canal system. The triple-blind, randomised clinical trial was conducted at the Department of Operative Dentistry and Endodontics, School of Dentistry, Shaheed Zulfiqar Ali Bhutto Medical University, Islamabad, Pakistan, from December 16, 2022, to June 15, 2023, and comprised patients having necrotic teeth and chronic apical pathosis. They were randomised into groups A and B. On the initial visit, after access opening and chemomechanical preparation, calcium hydroxide paste was placed as an intracanal medication in both groups. the patients were recalled after two weeks. In Group A, calcium hydroxide was removed from the canals using a rotary master apical file, while in Group B, an endoactivator was used to sonically agitate the endodontic irrigant. Verification of placement was done by using a periapical radiograph. Data was analysed using SPSS 26. Of the 98 individuals assessed initially, 60(61.22%) were included; 34(57%) females and 26(43%) males with age ranging from 19 to 57 years. There were 27(45%) incisors, 22(36.7%) premolars and 11(18.3%) canines. There were 30(50%) patients in each of the 2 groups. The intergroup difference was not statistically significant (p=0.43). Tooth arch did not significantly correlate with the removal method (p=0.79). Both methods were found to be equally effective in removing water-based calcium hydroxide medication from the endodontic system. NCT05744661.

Combination of Intracanal Medicines with Zinc Oxide Nanoparticles for Effective Eradication of Enterococcus faecalis

Background: Intracanal-resistant infections are the most important reason for root canal treatment failure. Therefore, cleaning the root canals is crucial. The efficiency of nanomedicines in eliminating intracanal contaminations and preventing bacterial attachment to surfaces are new strategies in this field. This study aimed to evaluate the effect of intracanal medicines, including calcium hydroxide (CH), zinc oxide nanoparticles (nZnO), pantoprazole (PP), and chlorhexidine (CHX) on Enterococcus faecalis (E. faecalis) in the individual and combinatorial form in an in vitro design in order to introduce an effective medicine for the eradication of E. faecalis. Sterilized water and sodium hypochlorite (NaOCl) 5.25% were used as the negative and positive control of antimicrobial activity, respectively. Methods: E. faecalis (ATCC 29212) was used for bacterial assays. The powder and the gel forms of the tested compounds were used in the analysis. The antibacterial and antibiofilm activities of the medicines were evaluated by the Minimum Inhibitory Concentration (MIC) determination using the broth microdilution method. The anti-biofilm effect of the tested compounds was assessed by Minimum Biofilm Inhibitory Concentration (MBIC). The antibacterial and antibiofilm effects of antimicrobial agent combinations were detected using the checkerboard assay and determination of the Fractional Inhibitory Concentration Index (FICI). Time-kill kinetics were conducted at zero, 2, 4, 6, 8, 10, 12, and 24 h. Results: Except for the MIC of the NaOCl, which was significantly lower than CH, there was no statistically significant difference between groups in MIC and MBIC. Only the mixture of CHX and nZnO and the mixture of PP and nZnO had a synergic effect against the planktonic and biofilm form of E. faecalis. Except for CHX and ZnO nanoparticles in gel form, other medicines did not show significant anti-biofilm effects against E. faecalis. Furthermore, the gel for CHX and nZnO showed stronger anti-biofilm effects. Conclusion: Combination therapy of common intracanal medicines with zinc oxide nanoparticles would lead to higher antibacterial and anti-biofilm effects against E. faecalis compared to conventional intracanal medicaments.

Smoked, smokeless, and poly-tobacco use during pregnancy in relation to infant mortality in Cambodia: Findings from a nationwide sample.

Maternal cigarette smoking during pregnancy is an established risk factor for adverse maternal, fetal, and infant outcomes. In contrast, maternal smokeless tobacco use (i.e. e-cigarettes, snus, betel quid, iqmik) during pregnancy has a more complex risk profile due to its potential use as a smoking cessation aid or to reduce the harm from smoking tobacco. The overall aim of this study was to investigate the association between smoked, smokeless, and poly-tobacco (smoked + smokeless) use during pregnancy and infant mortality, in a national sample of women in Cambodia. The study used data from the National Adult Tobacco Survey of Cambodia (NATSC) that employed sampling methods and tobacco survey items from the CDC Global Adult Tobacco Survey but also included a supplement on reproductive health and birthing history. We selected 5342 women of the NATSC who reported complete data on at least one pregnancy, and our unit of analysis was the 15998 pregnancies from these women. We conducted a multivariable logistic regression to relate tobacco use to infant mortality. Taylor linearized variance estimators were used to account for clustering by sampling unit and mother. We found that smokeless tobacco in the form of a betel quid was the most common form of tobacco used during pregnancy. In multivariable logistic regression, we found increased odds of infant death for all tobacco use categories (smoked, smokeless), but that the strongest effects were seen for habits that included smokeless tobacco (relative to never use of tobacco in any form): exclusive use of smokeless tobacco (adjusted odds ratio, AOR=2.08; 95% CI: 1.15-3.76), and poly-tobacco use (AOR=5.68; 95% CI: 1.03-31.46). In more detailed analyses that considered the composition of the betel quid (tobacco, areca nut/leaf, slaked lime), we found that even chewing of tobacco leaves with no processing or additives was associated with a three-fold increase in odds of infant death relative to a never user (AOR=3.05; 95% CI: 1.45-6.45). We found that even among those pregnant women who limited their nicotine habit to chewing tobacco leaves with no processing or additives, there remained higher odds of fetal or infant death from that pregnancy.

Efficacy of Glycyrrhizin as an Intracanal Medicament on Bacterial Load Reduction in Primary Infected Root Canals: A Randomized Clinical Trial.

This study was done to clinically investigate the efficacy of glycyrrhizin-based intracanal medication (ICM) compared to calcium hydroxide Ca(OH)2 and Ledermix on the bacterial counts inside the root canals of necrotic teeth with chronic periapical periodontitis. Thirty-six patients having single-rooted and single-canaled necrotic teeth with chronic periapical periodontitis were enrolled in this research. Aseptic control measures were taken before clinical steps. Access cavity preparation was done. First bacteriological samples (S1) were collected immediately after access cavity preparation and before cleaning and shaping inside the root canals. Cleaning and shaping were performed on the root canals. Patients were randomly allocated into 3 groups according to the type of intracanal medicament used [Ca(OH)2, Ledermix, Glycyrrhizin]. Second bacteriological samples (S2) were collected after 1 week from placing the ICMs. S1 and S2 were transferred to the lab of microbiology for culturing on blood agar dishes in anaerobic conditions, and the bacteria on the plates were enumerated as colony-forming units (CFUs) by the manual counting method. The anti-bacterial efficacy of the ICM was estimated by the percentage reduction in the bacterial colonies from S1 to S2. All tested ICM documented a significant reduction in the CFUs from S1 to S2 (p < 0.05). Regarding S1, there was no significant difference between the three tested materials (p > 0.05). Regarding S2, Glycyrrhizin and Ledermix showed significantly lower CFUs than Ca(OH)2. There was no significant difference between Glycyrrhizin and Ledermix. Under the conditions of the present study, Glycyrrhizin and Ledermix showed comparable antimicrobial effects that were better than the commonly used Ca(OH)2 ICM. Glycyrrhizin may be a promising ICM. Herbal medicine can be considered as an alternative antimicrobial material for root canal disinfection because it has many benefits, like low toxicity, absence of microbial resistance, and favorable antimicrobial efficacy. This study highlights the clinical efficacy of Glycyrrhizin as a promising ICM. How to cite this article: Eltantawi AR, Abdel-Razik GM, Elhawary YM, et al. Efficacy of Glycyrrhizin as an Intracanal Medicament on Bacterial Load Reduction in Primary Infected Root Canals: A Randomized Clinical Trial. J Contemp Dent Pract 2024;25(6):540-546.

Creep of Calcium Hydroxide from Stress-induced Dissolution: Kinetic Monte Carlo Simulations

Creep of Calcium Hydroxide from Stress-induced Dissolution: Kinetic Monte Carlo Simulations

Theoretical investigation on elastic property evolutions of low volume fly ash concrete

AbstractToward expanding the application of fly ash in cement‐based materials, this study proposes a comprehensive study on predicting the elastic properties of low‐volume fly ash concrete, with the replacement levels limited to 30% or less. Unlike conventional ordinary Portland cement concrete, the inclusion of fly ash in concrete brings alterations in properties from both chemical and physical perspectives: (1) the presence of fly ash liberates the alkaline solution that consumes calcium hydroxide to generate secondary calcium silicate hydrate gels; (2) unreacted fly ash particles exhibits a refinement effect on the micropore structure and contributes to forming a denser solid matrix. In order to characterize these effects on the mechanical properties of fly ash concrete, this paper conducts qualitative assessment of hydration reactions and quantitative calculations of volumetric compounds in the material. Utilizing the Mori‒Tanaka scheme, a predictive model is then developed to integrate the hierarchical effects of constituents at multiple scales on the modulus of elasticity of low‐volume fly ash concrete. The reliability of the proposed model is validated through a series of mechanical tests involving various mix designs, as well as comparison with other published test data.

Effect of non-thermal acidic and alkaline modifications on the structural, pasting, rheological, and functional properties of cassava (Manihot esculenta) starch.

This study aimed to investigate the effects of acid or alkali modification of isolated cassava starch (ICS) on its physicochemical properties. Acetic acid concentrations of 5%, 10%, and 20% v/v (0.87, 1.73, and 3.46M, respectively) and calcium hydroxide concentrations of 0.15%, 0.20%, and 0.30% w/w (0.02, 0.025, and 0.04M, respectively) were tested independently and compared with untreated isolated starch. The scanning electron microscope (SEM) shows starches with polyhedral and semispherical shapes; these modifications do not change the surface of the starch granules. Nanocrystals with orthorhombic crystal structure were extracted from ICS. Transmission electron microscopy (TEM) shows crystallites with a size (two-dimensional) of 20±5nm in length and 10±2nm in width and reveals that this starch contains nanocrystals with orthorhombic crystal structure. The X-ray patterns show that these nanocrystals are unaffected by acidic or alkaline treatments. The Ca+2 and CH3COO- ions do not interact with these nanocrystals. The alkaline treatment only affects the gelatinization temperature at a Ca(OH)2 concentration of 0.30%. Low concentrations of acidic and alkaline treatments affect the ability of cassava starch to absorb water and reduce the peak and final viscosity. The infrared spectra show that the modifications lead to C-H and C═C bond formations. ICS-B 0.30 can modify the amorphous regions of the starch, and the acid treatment leads to acetylation, which was confirmed by the presence of an IR band at 1740cm-1.

Preparation of nano magnesium oxide by mechanochemical method using magnesium chloride

Magnesium chloride is a magnesium resource that is widely present in seawater and salt lakes. Therefore, the use of magnesium chloride is of great significance for the low-cost preparation of high-performance magnesium materials. In this work, mechanical ball milling was used for the preparation of magnesium oxide nanoparticles from magnesium chloride. Ball milling improves the unevenness of the reaction process and generates magnesium oxide with a more uniform particle size distribution. First, a magnesium chloride complex was obtained by heating and evaporating a mixture of magnesium chloride and ethanol with a mass ratio of 1:2 at 110 °C. Next, pure magnesium hydroxide with a smaller crystal size was obtained by ball milling the prepared magnesium chloride complex with calcium hydroxide at 600 rpm for 3 h. Finally, the magnesium hydroxide was calcined at 1000 °C for 60 min to obtain nano magnesium oxide particles with a particle size of 670 nm.

Calcium carbonate is a liming product as good as calcium hydroxide in eutrophic CO2-rich waters

Currently, there is still much debate over the correct liming procedures to perform in shrimp ponds, concerning product, dosage, and timing, especially about the use of hydrated lime. The objective of this work was to determine the dissolution rates of Ca(OH)2 and CaCO3 in eutrophic CO2-rich waters with increasing Langelier saturation indexes (LSI), and discuss its importance to the rational liming of shrimp ponds. Three dilutions of seawater were prepared with increasing LSI values, namely −2.0, −1.0 and ≈ 0.0. The study was carried out in three consecutive phases of 5 weeks each. In the first, second and third phases, the flasks were filled with the LSI-2, LSI − 1 and LSI0 waters, respectively. In each phase, eight 2000-mL Erlenmeyer flasks received 1.0 g Ca(OH)2 p.a. and eight flasks received 1.0 g CaCO3 p.a. In four of the flasks that received Ca(OH)2 or CaCO3, one gram of a highly degradable organic matter (HDOM) was added. There were also four control flasks with no liming product but HDOM. The waters' temperature, pH, specific conductance, total alkalinity (TA), total hardness (TH), and the concentrations of Ca+2 and Mg+2 were monitored once a week. HDOM has moderated the increasing effect of Ca(OH)2 on the waters' pH. Regardless the water's LSI, and the liming product, the increase rate of TA was significantly greater in the HDOM-flasks. In all LSI-1 and LSI0 flasks, TH has decreased after the application of the liming products, despite the addition of HDOM. After one week, there was a marked Ca+2 drop in the Ca(OH)2 flasks with no HDOM. In all waters, the concentrations of Mg+2 have decreased significantly after the applications of Ca(OH)2 or CaCO3. Only the HDOM treatments have increased their initial LSI over time. The applications of Ca(OH)2 and CaCO3 in eutrophic CO2-rich waters have produced a total alkalinity higher than 100 mg L−1. Therefore, the anecdotal knowledge that hydrated lime is a superior liming product than agricultural limestone for shrimp ponds has not been supported by the present work.