Metal Content in Textile and (Nano)Textile Products

Metals, metallic compounds, and, recently, metallic nanoparticles appear in textiles due to impurities from raw materials, contamination during the manufacturing process, and/or their deliberate addition. However, the presence of lead, cadmium, chromium (VI), arsenic, mercury, and dioctyltin in textile products is regulated in Europe (Regulation 1907/2006). Metal determination in fabrics was performed by inductively coupled plasma-mass spectrometry (ICP-MS) after microwave-assisted acid digestion. The ICP-MS procedure has been successfully validated; relative standard deviations were up to 3% and analytical recoveries were within the 90–107% range. The developed method was applied to several commercial textiles, and special attention has been focused on textiles with nanofinishing (fabrics prepared with metallic nanoparticles for providing certain functionalities). Arsenic content (in textile T4) and lead content (in subsamples T1-1, T1-2, and T3-3) were found to exceed the maximum limits established by the European Regulation 1907/2006. Although impregnation of yarns with mercury compounds is not allowed, mercury was quantified in fabrics T1-2, T5, and T6. Further speciation studies for determining hexavalent chromium species in sample T9 are necessary (hexavalent chromium is the only species of chromium regulated). Some textile products commercialised in Europe included in this study do not comply with European regulation 1907/2006.

Chromium (VI) Inhibition of Low pH Bioleaching of Limonitic Nickel-Cobalt Ore

Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%.

Electrodeposition of Thick and Crack-Free Fe-Cr-Ni Coatings from a Cr (III) Electrolyte

The electrodeposition of iron-nickel-chromium coatings is a more environmentally friendly and economical alternative to hard-chrome coatings made from chromium (VI) electrolytes and stainless-steel bulk materials. The aim of the study was to develop a suitable deposition method for thick and low-crack Fe-Cr-Ni coatings. Iron-nickel-chromium coatings were electrodeposited using a more ecological chromium (III) electrolyte with direct current (DC), stepped direct current, and pulse current (PC). The influence of the deposition method on the electrolyte aging, the alloy composition of the coating, and their microstructure was investigated. Corrosion studies of the Fe-Cr-Ni coatings in 3.5% NaCl solution were performed using polarization tests. Furthermore, hardness measurements and scratch tests were carried out to determine the adhesion strength. Phase analyses were performed by X-ray diffraction, and the chemical composition and microstructure were characterized by scanning electron microscopy. Using the stepped DC and PC method, crack-free Fe-Cr-Ni coatings were successfully deposited.