Effects of Alkali on Water Soluble Hexavalent Chromium in Ordinary Portland Cement

Abstract

Due to the toxicity and mobility of chromium, the disposal of chromium-containing waste is a pressing issue. Co-processing of chromium-containing waste in a cement kiln is currently one of the most effective methods. However, the presence of water-soluble hexavalent chromium (Cr(VI)) in cement limits the use of this method. In this study, Na2CO3 was used to simulate alkali in industrial raw materials to investigate the pattern of influence of alkali content on water-soluble hexavalent chromium. The mechanisms associated with the oxidation and dissolution of chromium were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma emission spectrometry (ICP-OES). The proportion of Cr(VI) in the clinker detected by XPS increased rapidly with increasing alkali content. In the cement slurry system, alkali promotes more hexavalent chromium leaching by influencing pH and other ion concentrations (Ca2+, SO42−). Therefore, the addition of alkali to either the raw meal or to the cement slurry system will favour an increase in the water-soluble Cr(VI) content. This study may provide theoretical guidance for the preparation and use of clinkers containing chromium.

“Gamma Irradiation Synthesis of Carboxymethyl Chitosan-Nanoclay Hydrogel for the Removal of Cr(VI) and Pb(II) from Aqueous Media”

“…On the other hand, the thermal stability of the composite is enhanced with the addition of clay particles due to its high crystallinity [77]. Some investigators attributed the improved thermal stability of the composite due to the strong electrostatic attraction between the anionic groups of modified chitosan and the cationic metals in the clay molecule [78].…”

“…The effect of pH was verified by the batch model in a range varied from 1.0 to 9.0 for Pb (II) cations and from 4.0 to11.0 for Cr (VI) cations using fixed conditions of 50 mg adsorbent, 2 h contact time, and 50 ml aqueous solution evaluating 100 mg/L Cr (VI) or Pb (II) cations at ambient temperature. The pH range for conducting the experiments was carefully selected according to the degree of solubility of each cation as per previous works [77,78]. The maximum metal uptake performance was attained at pH 8.0 for Pb (II) and pH 9.0 for Cr (VI), according to the data displayed in Fig.…”