Recycling of chromium wastes from the tanning industry to produce ceramic nanopigments

Growth in the use of colored ceramics and the demand for better quality have stimulated research into the development of new classes of pigments with superior durability and color reproducibility, which can be produced using inexpensive, straightforward, and eco-friendly synthesis procedures.

Transmission Electron Microscopy (TEM) Through Focused ION Beam (FIB) from Vitrified Chromium Wastes

This study shows how the Focused Ion Beam (FIB) has been applied to vitrified materials obtained from chromiumwastes. Due to the issues arising during conventional Ar+ ion milling, it was necessary to thin these samples usingFIB. Difficulties came from the heterogeneous size between chromium spinels and the residual glass phase. The FIBwas applied to obtain thin foils from vitrified materials. These brittle and heterogeneous samples result in specimenswith many perforations and chipping when using conventional thinning below 100 nanometers. Alternatively, FIBallowed thinning in the range of 60 - 80 nanometers from specifically selected areas such as the areas containingspinel crystals Mg(Al,Cr)2O4 in order to facilitate the final Transmission Electron Microscopy (TEM) observations. Inthis paper, FIB is shown to be a very powerful microtool as a brittle samples preparation method as well as providingan alternative way for performing conventional ceramography and Ar+ ion milling. FIB is a much less destructivemethod with greater observed capacity in the quantity and analysis of microcrystalline phases.

Treatment Strategy for Cr(VI)-Bearing Wastes

The effects of reductants and alkali on the sludge quantity of chromium wastes and the teachability and physical properties of solidified chromium matrix are investigated in this study. FeSO4 and NaHSO3 are model reductants, and NaOH and Ca(OH)2 serve as bases, respectively. Portland cement was used to solidify Cr sludges generated from real wastes. Results from potentiometric redox titration showed that a 99.9% destruction of Cr(VI) at equivalence point is not achievable unless additional dosage is imposed. The extra amounts of reducing agent necessary for 99.9% conversion of Cr(VI) to Cr(III) is dependent on system parameters such as pH and type of reductants applied. An increase in operating pH where redox proceeds may acquire much more reducing chemicals than lower pH does. The optimum pH range for maximum precipitation is from 8.5 to 9.0. Chromium sludges generated from synthetic wastewater have a specific resistance from 8.7×l011 to 1.28×l013 m/kg. The use of Ca(OH)2 as base to precipitate Cr(III) produces sludge with lower specific resistance and larger particle size (near 20 to 60 µm). When examined with TCLP test, the chromium leachated out to the solution from matrix is generally less than 1 mg/L. Compressive strength of solidified sludge can reach near 10 kg/cm2 in 3 days based on 1:1 sludge/cement ratio. The compressive strength is affected by the type of reductants as well as the bases employed in the wastewater treatment processes. To producc a matrix with better compressive strength, it is recommended to use FeSO4 along with Ca(OH)2; however, if NaOH is used to control system pH, NaHSO3 is suggested to serve as reductant.