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Copper flotation tailings (FTs), resulting from the separation and beneficiation processes of ores, are a significant source of environmental pollution (acid mine drainage, toxic elements leaching, and dust generation). The most common disposal method for this industrial waste is dumping. However, due to their favorable physical and chemical properties—the high content of aluminosilicate minerals (60–90%)—flotation tailings can be effectively treated and reused through geopolymerization technology, thereby adding value to this waste. The objective of this study was to evaluate the potential of utilizing the geopolymerization of FTs to produce sustainable materials. Geopolymers based on natural zeolite (NZ), sodium-modified natural zeolite (NaZ), and fly ash (FA) were prepared using 20%, 35%, and 50% of FTs, activated with a 10 M NaOH solution. The study investigated the influence of Ca/Si, Si/Al, and Na/Al molar ratios on the structural, thermal, and mechanical properties (XRD, TG/DTG and unconfined compressive strength, UCS), and contaminant immobilization (TCLP method) of geopolymers. Geochemical modeling via the PHREEQC program was employed to interpret the results. The findings indicated that the UCS value decreased in zeolite-based geopolymers as the content of FT increased due to the inertness of the tailings and the low calcium content in the system (Ca/Si ≤ 0.3), in contrast to the FA-based geopolymer. The highest UCS of 44.3 MPa was recorded in an FA-based geopolymer containing 50% flotation tailings, with optimal molar ratios of 0.4 for Ca/Si, 3.0 for Si/Al, and 1.1 for Na/Al. In conclusion, the geopolymerization process has been determined to be a suitable technological approach for the sustainable treatment and reuse of FTs. [ABSTRACT FROM AUTHOR]

Due to the development of resistance to antimicrobial agents, bacterium Acinetobacter baumannii is nowadays a leading cause of nosocomial outbreaks. Clinically relevant A. baumannii outside hospital settings including natural soils affected by human waste represents a public-health risk for humans and animals. The aim of this study was to investigate the potential of metal-loaded zeolites to eliminate viable A. baumannii from artificially contaminated natural soils. A. baumannii isolate was subjected to the activity of natural zeolitised tuff (NZ) and Cu-modified (CuNZ) or Ag-modified zeolite (AgNZ) in wet, slightly acidic terra rossa and slightly alkaline red palaeosol. A. baumannii survived in terra rossa and red palaeosol supplemented with 1 wt% of NZ for seven days and four months, respectively. The addition of 1 wt% of CuNZ to terra rossa and red palaeosol shortened the survival of A. baumannii to three and 14 days, respectively. The addition of 0.1 wt% of AgNZ to both soils resulted in complete removal of viable A. baumannii within 1 h of contact, while the total native heterotrophic bacterial counts remained high. Since AgNZ is prepared with a simple modification of cost-effective and environmentally friendly natural zeolite, it is a promising material for the remediation of soils contaminated with pandrug-resistant A. baumannii.

Chitosan/gelatin and chitosan/gelatin/zeolite films prepared by solvent casting method are impregnated with a mixture of thymol and carvacrol using a green solvent, supercritical carbon dioxide at 35 °C and 30 MPa, during 18 h. Proposed method enables preparation of biocompatible and biodegradable blends with strong antioxidant and antibacterial activity, whereby amounts of loaded thymol/carvacrol (TC) mixture are in the range from 3.3% to 6%. After initial burst release, both types of films exhibit gradual release of bioactive compounds, with around 72% and 96% of impregnated TC mixture released in water and phosphate buffered saline solution (pH 7.4) during tested period of 10 days, respectively. Results of water vapor transmission rate (>76 g m−2 day−1) confirm that prepared composites are suitable for wound dressing application. Thermal analysis shows superior properties of prepared TC loaded films compared to control samples. In addition, mechanical and structural properties, as well as solubility and swelling behavior of the obtained films are investigated in detail. [ABSTRACT FROM AUTHOR]

Due to the development of resistance to antimicrobial agents, bacterium Acinetobacter baumannii is nowadays a leading cause of nosocomial outbreaks. Clinically relevant A. baumannii outside hospital settings including natural soils affected by human waste represents a public-health risk for humans and animals. The aim of this study was to investigate the potential of metal-loaded zeolites to eliminate viable A. baumannii from artificially contaminated natural soils. A. baumannii isolate was subjected to the activity of natural zeolitised tuff (NZ) and Cu-modified (CuNZ) or Ag-modified zeolite (AgNZ) in wet, slightly acidic terra rossa and slightly alkaline red palaeosol. A. baumannii survived in terra rossa and red palaeosol supplemented with 1 wt% of NZ for seven days and four months, respectively. The addition of 1 wt% of CuNZ to terra rossa and red palaeosol shortened the survival of A. baumannii to three and 14 days, respectively. The addition of 0.1 wt% of AgNZ to both soils resulted in complete removal of viable A. baumannii within 1 h of contact, while the total native heterotrophic bacterial counts remained high. Since AgNZ is prepared with a simple modification of cost-effective and environmentally friendly natural zeolite, it is a promising material for the remediation of soils contaminated with pandrug-resistant A. baumannii. [ABSTRACT FROM AUTHOR]

Antibacterial activity of a natural zeolite, clinoptilolite (Z), enriched with about 0.4-0.5 mmol of Ag (Ag-Z), Cu (Cu-Z) or Zn (Zn-Z) was tested toward two strains of Gram-negative bacteria - Escherichia coli and Acinetobacter baumannii - in natural seawater from Adriatic Sea (Croatia). The Ag-Z and Cu-Z exhibited bactericidal activity toward E. coli and A. baumannii after 3 and 6 h of exposure, respectively. The Zn-Z showed antibacterial activity toward both strains, but lacking the bactericidal effect even after 24 h of exposure. All studied samples released metal cations in seawater. Concentration of Ag and Zn leached from Ag-Z and Zn-Z was higher than maximum allowable concentrations (MAC) for drinking water, whereas concentration of Cu was below MAC. Due to high concentration of Na+ in seawater (about 1.2 g Na+ dm-3) an ion-exchange process can be responsible for the leaching of the studied cations. The lowest extent of leaching from Cu-Z was ascribed to different position and geometry of sites occupied by Cu(II) in the clinoptilolite lattice. The antibacterial activity of M-Z was attributed to the metal cations leached from the zeolite lattice into seawater. The obtained results indicate that Cu-Z can be considered as a promising disinfectant for treatment of seawater. [ABSTRACT FROM AUTHOR]

The adsorption of the antibiotic ciprofloxacin (CIP) from an aqueous solution by natural zeolite, the calcium-rich clinoptilolite (CLI), and magnetite-coated CLI (MAG-CLI) was investigated. Both CLI and MAG-CLI showed a high adsorption affinity towards CIP at 283, 288 and 293 K at a pH of 5. Adsorption kinetics studied for the initial concentrations of 15–75 mg CIP dm−3 follow Lagergren's pseudo-second order equation and the adsorption is best represented by the Langmuir model. The adsorption mechanism involves strong electrostatic interactions between negatively charged aluminosilicate lattice and the cationic form of CIP accompanied by an ion-exchange reaction. Magnetite coverage (approx. 12 wt.%) induces magnetism, which can facilitate the separation process. The coverage does not influence the adsorption activity of CLI. The leaching test showed that the MAG coating protects the adsorbent from CIP leaching. This is ascribed to interactions between the CIP carboxyl groups and magnetite nano-particles. Antibacterial tests showed strong antibacterial activity of the ciprofloxacin-containing adsorbents towards pathogenic E. coli and S. aureus. [ABSTRACT FROM AUTHOR]

In the present study, supercritical solvent impregnation (SSI) has been applied to incorporate thymol into bio-composite polymers as a potential active packaging material. Thymol, a natural component with a proven antimicrobial activity, was successfully impregnated into starch-chitosan (SC) and starch-chitosan-zeolite (SCZ) films using supercritical carbon dioxide (scCO2) as a solvent. Experiments were performed at 35 °C, pressures of 15.5 and 30 MPa, and an impregnation time in the range of 4–24 h. The highest impregnation yields of SC films with starch to chitosan mass ratios of 1:1 and 1:2 were 10.80% and 6.48%, respectively. The addition of natural zeolite (15–60%) significantly increased the loading capacity of films enabling thymol incorporation in a quantity of 16.7–27.3%. FTIR and SEM analyses were applied for the characterization of the films. Mechanical properties and water vapor permeability of films before and after the impregnation were tested as well. Thymol release kinetics in deionized water was followed and modeled by the Korsmeyer-Peppas and Weibull model. SCZ films with thymol loading of approximately 24% exhibited strong antibacterial activity against E. coli and methicillin-resistant Staphylococcus (S.) aureus (MRSA). [ABSTRACT FROM AUTHOR]