Low concentrated phosphorus sorption in aqueous medium on aragonite synthesized by carbonation of seashells: Optimization, kinetics, and mechanism study.

Phosphorus (P) concentration beyond threshold limit can trigger eutrophication in stagnant water bodies nevertheless it is an indispensable macronutrient for aquatic life. Even in low P concentration (≤1 mg L-1), P can be detrimental for ecosystem's health, but this aspect has not been thoroughly investigated. The elimination of low P content is rather expensive or complex. Therefore, a unique and sustainable approach has been proposed in which valorized bivalve seashells can be used for the removal of low P content. Initially, acicular shaped aragonite particles (~21 µm) with an aspect ratio of around 21 have been synthesized through the wet carbonation process and used to treat aqueous solutions containing P in low concentration (P ≤ 1 mg L-1). Response surface methodology based Box-Behnken design has been employed for optimization study which revealed that with aragonite dosage (140 mg), equilibrium pH (~10.15), and temperature (45 °C), a phosphorus removal efficiency of ~97% can be obtained in 10 h. The kinetics and isotherm studies have also been carried out (within the range P ≤ 1 mg L-1) to investigate a probable removal mechanism. Also, aragonite demonstrates higher selectivity (>70%) towards phosphate with coexisting anions such as nitrate, chloride, sulfate, and carbonate. Through experimental data, elemental mapping, and molecular dynamic simulation, it has been observed that the removal mechanism involved a combination of electrostatic adsorption of Ca2+ ions on aragonite surface and chemical interaction between the calcium and phosphate ions. The present work demonstrates a sustainable and propitious potential of seashell derived aragonite for the removal of low P content in aqueous solution along with its unconventional mechanistic approach.

Environmental benign synthesis, characterization and mechanism studies of green calcium hydroxide nano-plates derived from waste oyster shells.

Continuous dumping of oyster shells in open fields has been a global issue, causing serious problems in the water and human health. The conversion of those wastes into value-added products is highly desirable. Here, Green Calcium Hydroxide Nano-plates (GCHNPs) were first synthesized from waste oyster shells by a chemical precipitation method in an aqueous medium at 90 °C without using any additives. The crystal structure with a hexagonal portlandite (Ca(OH)2) was observed by both X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The crystal size of around 350-450 nm and specific surface area with 4.96 m2g-1 were confirmed by field emission scanning electron microscopy (FE-SEM) and Brunauer-Emmett-Teller (BET), respectively. In addition, a schematically organized new qualitative model for a mechanism was proposed to explain the genesis and evolution of GCHNPs from raw oyster shells.

Aqueous Nd3+ capture using a carboxyl-functionalized porous carbon derived from ZIF-8.

A porous graphitic carbon was obtained via the pyrolysis of a zeolite imidazolate framework (ZIF-8) under Ar atmosphere. Then, the carbon was functionalized with carboxylic groups and applied for separation of neodymium ions (Nd3+) from water. The adsorbent (denoted as C-ZDC) was characterized by X-ray diffraction, N2 adsorption-desorption isotherms, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning and transition electron microscopies, thermogravimetric analysis, and Boehm titration. A practical adsorption equilibrium was attained within 4 h, and the adsorption isotherm at 25 °C revealed a maximum adsorption capacity of 175 mg/g, which is one of the highest values reported for different kinds of adsorbents. The adsorption kinetics and equilibrium isotherms were modeled, and the selectivity for Nd3+ over other metal ions was examined. From the effect of solution pH on the adsorption and material characterization results before and after adsorption, the high adsorption capacity of C-ZDC was ascribed to the formation of coordination bonds between Nd3+ ions and the -COOH groups. Further, the material was reusable for at least four adsorption-desorption cycles after a simple step of acid washing.

Identification of Calcium Sulphoaluminate Formation between Alunite and Limestone.

This study was carried out to identify the conditions of formation of calcium sulphoaluminate (3CaO·3Al(2)O(3)·CaSO(4)) by the sintering of a limestone (CaCO(3)) and alunite [K(2)SO(4)·Al(2)(SO(4))(3)·4Al(OH)(3)] mixture with the following reagents: K(2)SO(4), CaCO(3), Al(OH)(3), CaSO(4)·2H(2)O, and SiO(2). When K(2)SO(4), CaCO(3), Al(OH)(3), CaSO(4)·2H(2)O were mixed in molar ratios of 1:3:6:3 and sintered at 1,200∼1,300 °C, only 3CaO·3Al(2)O(3)·CaSO(4) and calcium langbeinite (2CaSO(4)·K(2)SO(4)) were generated. With an amount of CaO that is less than the stoichiometric molar ratio, 3CaO·3Al(2)O(3)·CaSO(4) was formed and anhydrite (CaSO(4)) did not react and remained behind. With the amount of CaSO(4) that is less than the stoichiometric molar ratio, the amounts of 3CaO·3Al(2)O(3)·CaSO(4) and 2CaSO(4)·K(2)SO(4) decreased, and that of CaO·Al(2)O(3) increased. In the K(2)SO(4)-CaO-Al(2)O(3)-CaSO(4)-SiO(2) system, to stabilize the formation of 3CaO·3Al(2)O(3)·CaSO(4), 2CaSO(4)·K(2)SO(4), and ß-2CaO·SiO(2), the molar ratios of CaO: Al(2)O(3): CaSO(4) must be kept at 3:3:1 and that of CaO/SiO(2), over 2.0; otherwise, the generated amount of 3CaO·3Al(2)O(3)·CaSO(4) decreased and that of gehlenite (2CaO·Al(2)O(3)·SiO(2)) with no hydration increased quantitatively. Therefore, if all SO(3)(g) generated by the thermal decomposition of alunite reacts with CaCO(3) (or CaO, the thermal decomposition product of limestone) to form CaSO(4) in an alunite- limestone system, 1 mol of pure alunite reacts with 6 mol of limestone to form 1 mol of 3CaO·3Al(2)O(3)·CaSO(4) and 1 mol of 2CaSO(4)·K(2)SO(4).

Effect of hydraulic activity on crystallization of precipitated calcium carbonate (PCC) for eco-friendly paper.

Wt% of aragonite, a CaCO(3) polymorph, increased with higher hydraulic activity ( degrees C) of limestone in precipitated calcium carbonate (PCC) from the lime-soda process (Ca(OH)(2)-NaOH-Na(2)CO(3)). Only calcite, the most stable polymorph, was crystallized at hydraulic activity under 10 degrees C, whereas aragonite also started to crystallize over 10 degrees C. The crystallization of PCC is more dependent on the hydraulic activity of limestone than CaO content, a factor commonly used to classify limestone ores according to quality. The results could be effectively applied to the determination of polymorphs in synthetic PCC for eco-friendly paper manufacture.

Effect of Eggshell Powder on the Hydration of Cement Paste.

Eggshells are one of the solid wastes in the world and are considered hazardous according to European Commission regulations. The utilization of solid wastes, like eggshells, will help create a sustainable environment by minimizing the solid wastes that are disposed into the environment. The utilization of eggshell powder in cement also helps to reduce the carbon dioxide emissions from cement factories by reducing clinker production. In this study, the effect of eggshell powder on the hydration of cement products was investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Pastes were made with 10% and 20% eggshell powder and examined for 1, 14, and 28 days of hydration. The addition of eggshell powder transformed ettringite to monosulfoaluminate and to monocarboaluminate. In 20% eggshell powder, the formation of monocarboaluminate was detected in the early stages and accelerated the hydration reaction. The CaCO3 from the eggshells reacted with the C3A and changed the hydration products of the pastes. The addition of eggshell powder provided nucleation sites in the hydration products and accelerated cement hydration.

Aggravation of Human Diseases and Climate Change Nexus.

For decades, researchers have debated whether climate change has an adverse impact on diseases, especially infectious diseases. They have identified a strong relationship between climate variables and vector's growth, mortality rate, reproduction, and spatiotemporal distribution. Epidemiological data further indicates the emergence and re-emergence of infectious diseases post every single extreme weather event. Based on studies conducted mostly between 1990-2018, three aspects that resemble the impact of climate change impact on diseases are: (a) emergence and re-emergence of vector-borne diseases, (b) impact of extreme weather events, and (c) social upliftment with education and adaptation. This review mainly examines and discusses the impact of climate change based on scientific evidences in published literature. Humans are highly vulnerable to diseases and other post-catastrophic effects of extreme events, as evidenced in literature. It is high time that human beings understand the adverse impacts of climate change and take proper and sustainable control measures. There is also the important requirement for allocation of effective technologies, maintenance of healthy lifestyles, and public education.

Environmental remediation and conversion of carbon dioxide (CO(2)) into useful green products by accelerated carbonation technology.

This paper reviews the application of carbonation technology to the environmental industry as a way of reducing carbon dioxide (CO(2)), a green house gas, including the presentation of related projects of our research group. An alternative technology to very slow natural carbonation is the co-called 'accelerated carbonation', which completes its fast reaction within few hours by using pure CO(2). Carbonation technology is widely applied to solidify or stabilize solid combustion residues from municipal solid wastes, paper mill wastes, etc. and contaminated soils, and to manufacture precipitated calcium carbonate (PCC). Carbonated products can be utilized as aggregates in the concrete industry and as alkaline fillers in the paper (or recycled paper) making industry. The quantity of captured CO(2) in carbonated products can be evaluated by measuring mass loss of heated samples by thermo-gravimetric (TG) analysis. The industrial carbonation technology could contribute to both reduction of CO(2) emissions and environmental remediation.

Leachability of arsenic and heavy metals from mine tailings of abandoned metal mines.

Mine tailings from an abandoned metal mine in Korea contained high concentrations of arsenic (As) and heavy metals [e.g., As: 67,336, Fe: 137,180, Cu: 764, Pb: 3,572, and Zn: 12,420 (mg/kg)]. US EPA method 6010 was an effective method for analyzing total arsenic and heavy metals concentrations. Arsenic in the mine tailings showed a high residual fraction of 89% by a sequential extraction. In Toxicity Characteristic Leaching Procedure (TCLP) and Korean Standard Leaching Test (KSLT), leaching concentrations of arsenic and heavy metals were very low [e.g., As (mg/L): 0.4 for TCLP and 0.2 for KSLT; cf. As criteria (mg/L): 5.0 for TCLP and 1.5 for KSLT].