Clam shell waste recycling and valorization for sustainable Hg remediation.

Shellfish aquaculture world production is constantly growing due to the increase in demand for seafood and reached over 18 million tons in 2022. The suitable management of the shell waste is one of the main environmental challenging issues as most of this waste is sent to landfills with emanation of foul odors, pathogens proliferation and reduction of available space. However, the conversion of this biowaste to new value-added materials could provide significant environmental and economic benefits. Clam shell waste was the starting material for the synthesis of hydroxyapatite (CSHAP) applied as an adsorbent for Hg2+ removal from aqueous solutions. Adsorption experiments were performed in batch using simulated wastewaters prepared from HgCl2 to investigate the effects of contact time and initial Hg2+ concentration on the removal process. Mineralogical composition, morphological features and elemental composition of CSHAP before and after the experiments were investigated by XRPD, SEM-EDS and FTIR analysis. The concentrations of Hg2+ and Ca2+ in the solutions were analyzed by ICP-AES. The adsorption kinetics of Hg2+ was simulated with the pseudo-first-order rate model, the pseudo-second order model and the intraparticle diffusion model. The results of the kinetics study showed that the Hg2+ adsorption followed the pseudo-second-order kinetics model and reached equilibrium within 40 min. The Langmuir model fitted the experimental results better than the Freundlich, Temkin and Dubinin-Radushkevic isotherm models, with a maximum adsorption capacity of 65.8 mg/g which is generally higher than other waste-derived adsorbents used for the removal of Hg2+ ions from water. The removal mechanism includes rapid surface complexation on CSHAP grains, followed by a slow incorporation of the Hg2+ ions in the crystalline structure. The results of this study could contribute to delineate a new research direction for a more sustainable management of clam shell biowaste.

The blue road: Provenance study of azurite samples from historical locations through the analysis of minor and trace elements.

The pigments used by artists since ancient times play an important role in historical, artistic, and cultural investigations. They allow the acquisition of useful information for the study of human and technological development. This research aims at differentiating the various sources of azurite exploited in antiquity, based on the study of minor and trace elements. Azurite is one of the most important blue pigments in art history, widely used during the Middle Age and Renaissance. However, very few studies investigated the provenance of the pigment, so today it is still not possible to clearly identify the sources of azurite exploited in the past. This study is based on the analysis of several samples of azurite belonging to the MUST collection (Museum of Earth Sciences, Sapienza University of Rome, Italy) and coming from different historical localities: UK, Italy, Germany, France, Romania and Slovakia (both representative of the resources within the ancient Kingdom of Hungary), Greece and Russia. The samples were analysed by electron microscopy (EMPA and SEM-EDX) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), with the aim of detecting chemical features that are specific to the different azurite ore deposits. Among the trace elements analysed, Zn, As, Sn, Ca and Sr prove the most suitable for discriminating the origin of the samples, as well as rare earth elements. In particular, Ce and Eu anomalies are suggested as markers for the German and Hungarian localities.

Preparation of Hydrogel Composites Using a Sustainable Approach for In Situ Silver Nanoparticles Formation.

The recognized antibacterial properties of silver nanoparticles (AgNPs) characterize them as attractive nanomaterials for developing new bioactive materials less prone to the development of antibiotic resistance. In this work, we developed new composites based on self-assembling Fmoc-Phe3 peptide hydrogels impregnated with in situ prepared AgNPs. Different methodologies, from traditional to innovative and eco-sustainable, were compared. The obtained composites were characterized from a hydrodynamic, structural, and morphological point of view, using different techniques such as DLS, SEM, and rheological measurements to evaluate how the choice of the reducing agent determines the characteristics of AgNPs and how their presence within the hydrogel affects their structure and properties. Moreover, the antibacterial properties of these composites were tested against S. aureus, a major human pathogen responsible for a wide range of clinical infections. Results demonstrated that the hydrogel composites containing AgNPs (hgel@AgNPs) could represent promising biomaterials for treating S. aureus-related infections.

Green In Situ Synthesis of Silver Nanoparticles-Peptide Hydrogel Composites: Investigation of Their Antibacterial Activities.

The present paper investigated the synthesis of peptide-based hydrogel composites containing photo-generated silver nanoparticles (AgNPs) obtained in the presence and absence of honey as tensile strength enhancer and hydrogel stabilizer. Fmoc-Phe and diphenylalanine (Phe2) were used as starting reagents for the hydrogelator synthesis via an enzymatic method. In particular, we developed an in situ one-pot approach for preparing AgNPs inside peptide hydrogels using a photochemical synthesis, without any toxic reducing agents, with reaction yields up to 30%. The structure and morphology of the nanohybrids were characterized with different techniques such as FESEM, UV-Vis, DLS, SAXS and XPS. Moreover, the antibacterial activity of these hybrid biomaterials was investigated on a laboratory strain and on a clinical isolate of Staphylococcus aureus. Results demonstrated that honey increased both swelling ability and also mechanical stability of the hydrogel. Finally, a higher antibacterial effect of AgNPs in the hybrid was observed in the presence of honey. In particular, AgNPs/hgel and AgNPs/hgel-honey showed an enhanced antibacterial activity (3.12 mg/L) compared to the free form of AgNPs, alone or in combination with honey (6.25 mg/L) for both S. aureus strains.

Valorization of Eggshell Biowaste for Sustainable Environmental Remediation.

The management of large amounts of eggshell waste annually produced in the world is problematic as generally this material is only disposed at landfills with odor production and microbial growth. On the contrary, significant environmental and economic advantages could be obtained transforming this biowaste into new value-added products. Eggshell biowaste was the starting material for the synthesis of hydroxyapatite by a simple and sustainable procedure and applied for the removal of Co2+ from aqueous solutions. The effects of contact time and initial metal concentration were investigated in batch experiments. Eggshell-based hydroxyapatite (ESHAP) before and after Co2+ removal was characterized by X-ray diffraction and scanning electron microscopy. The process was rapid and reached equilibrium within 80 min. The removal efficiency was in the range 70-80% which is generally higher than other waste-derived adsorbents. Adsorption of Co2+ on the surface of ESHAP particles and ion exchange with Ca2+ resulting in the formation of a Co-phosphate are the main mechanisms of the metal removal. The conversion of eggshell waste to a low-cost adsorbent for the treatment of metal contaminated waters could contribute to a more sustainable and effective management of this biowaste.

Evaluation of the effectiveness of phosphate treatment for the remediation of mine waste soils contaminated with Cd, Cu, Pb, and Zn.

The effectiveness of phosphate treatment for Cd, Cu, Pb, and Zn immobilization in mine waste soils was examined using batch conditions. Application of synthetic hydroxyapatite (HA) and natural phosphate rock (FAP) effectively reduced the heavy metal water solubility generally by about 84-99%. The results showed that HA was slightly superior to FAP for immobilizing heavy metals. The possible mechanisms for heavy metal immobilization in the soil involve both surface complexation of the metal ions on the phosphate grains and partial dissolution of the phosphate amendments and precipitation of heavy metal-containing phosphates. HA and FAP could significantly reduce Cd, Cu, Pb, and Zn availability in terms of water solubility in contaminated soils while minimizing soil acidification and potential risk of eutrophication associated with the application of highly soluble phosphate sources.

The thermal behaviour and structural stability of nesquehonite, MgCO3.3H2O, evaluated by in situ laboratory parallel-beam X-ray powder diffraction: New constraints on CO2 sequestration within minerals.

In order to gauge the appropriateness of CO(2) reaction with Mg chloride solutions as a process for storing carbon dioxide, the thermal behaviour and structural stability of its solid product, nesquehonite (MgCO(3).3H(2)O), were investigated in situ using real-time laboratory parallel-beam X-ray powder diffraction. The results suggest that the nesquehonite structure remains substantially unaffected up to 373 K, with the exception of a markedly anisotropic thermal expansion acting mainly along the c axis. In the 371-390 K range, the loss of one water molecule results in the nucleation of a phase of probable composition MgCO(3).2H(2)O, which is characterized by significant structural disorder. At higher temperatures (423-483 K), both magnesite and MgO.2MgCO(3) coexist. Finally, at 603 K, periclase nucleation starts and the disappearance of carbonate phases is completed at 683 K. Consequently, the structural stability of nesquehonite at high temperatures suggests that it will remain stable under the temperature conditions that prevail at the Earth's surface. These results will help (a) to set constraints on the temperature conditions under which nesquehonite may be safely stored and (b) to develop CO(2) sequestration via the synthesis of nesquehonite for industrial application.

Synthesis of nesquehonite by reaction of gaseous CO2 with Mg chloride solution: its potential role in the sequestration of carbon dioxide.

In this paper is reported a novel method to synthesize nesquehonite, MgCO(3) x 3H(2)O, via reaction of a flux of CO(2) with Mg chloride solution at 20+/-2 degrees C. The reaction rate is rapid, with carbonate deposition almost complete in about 10 min. The full characterization of the product of synthesis has been performed to investigate its potential role as a "CO(2)-sequestering medium" and a means of disposing Mg-rich wastewater. We investigated the nesquehonite synthesized using SEM, XRD, FTIR and thermal analysis. The thermodynamic and chemical stability of this low-temperature hydrated carbonate of Mg and its possible transformation products make our method a promising complementary solution to other methods of CO(2) sequestration. Carbonation via magnesium chloride aqueous solutions at standard conditions represents a simple and permanent method of trapping CO(2). It could be applied at point sources of CO(2) emission and could involve rejected brine from desalination plants and other saline aqueous wastes (i.e., "produced water"). The likelihood of using the resulting nesquehonite and the by-products of the process in a large number of applications makes our method an even more attractive solution.

Cadmium removal from single- and multi-metal (Cd + Pb + Zn + Cu) solutions by sorption on hydroxyapatite.

Heavy metal contamination of waters and soils is particularly dangerous to the living organisms. Different studies have demonstrated that hydroxyapatite has a high removal capacity for divalent heavy metal ions in contaminated waters and soils. The removal of Cd from aqueous solutions by hydroxyapatite was investigated in batch conditions at 25+/-2 degrees C. Cadmium was applied both as single- or multi-metal (Cd + Pb + Zn + Cu) systems with initial concentrations from 0 to 8 mmol L(-1). The adsorption capacity of hydroxyapatite in single-metal system ranged from 0.058 to 1.681 mmol of Cd/g of hydroxyapatite. In the multi-metal system competitive metal sorption reduced the removal capacity by 63-83% compared to the single-metal system. The sorption of Cd by hydroxyapatite follows the Langmuir model. Cadmium immobilization occurs through a two-step mechanism: rapid surface complexation followed by partial dissolution of hydroxyapatite and ion exchange with Ca resulting in the formation of a cadmium-containing hydroxyapatite.

Copper and zinc decontamination from single- and binary-metal solutions using hydroxyapatite.

Toxic metals contamination of waters, soils and sediments can seriously affect plants, animals and human being. The bioavailability of metal ions can be reduced trapping them in minerals with low solubilities. This study investigated the sorption of aqueous Cu and Zn onto hydroxyapatite surfaces. Batch experiments were carried out using synthetic hydroxyapatite. The metals were applied as single or binary species, in a range of metal concentrations ranging from 0 to 8 mmol/L at 25+/-2 degrees C. The removal capacity of hydroxyapatite was 0.016-0.764 mmol of Cu/g and 0.015-0.725 mmol of Zn/g. In the Cu-Zn binary system, competitive metal sorption occurred with reduction of the removal capacity by 13-76% and 10-63% for Cu and Zn, respectively, compared to the single-metal systems. The sorption of Cu and Zn was well characterized by the Langmuir model. Heavy metal immobilization was attributed to a two-step mechanism: first rapid surface complexation and secondly partial dissolution of hydroxyapatite and ion exchange with Ca followed by the precipitation of a heavy metal-containing hydroxyapatite.