Abstract
The removal of azo dyes is a critical issue in current textile industry wastewater treatment. In contemporary wastewater management, many structures that are in direct contact with wastewater are constructed with concrete. In this contribution, the removal of Congo red from aqueous solutions by the material in the surface of hardened binder paste was studied in multiple exposure experiments. Flat prisms made with ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBS) were stored in different aqueous solutions. The powdered surface material of these flat prisms was used as a substrate for the removal of Congo red from aqueous solutions. Storage in sodium sulfate solution lead to the formation of hydrotalcite nanosheets on the surfaces of hardened binder pastes rich in magnesium provided by the GGBS. These nanosheets resulted in a large specific surface area and increased the discoloration capacity with respect to binder mass. The results also suggest that the carbonation of ettringite and C-S-H can provide fresh calcite that can act as a secondary adsorbent. The results of this study suggest that cementitious binders with high magnesium contents could contribute to the removal of azo dyes from industrial wastewater by providing economically attractive treatment materials.
Highlights
Synthetic dyes are commonly used in textile, cosmetics and other industries
The composition of the layered double hydroxides (LDH) phases being formed in hardened binder paste is likely to be controlled by the composition of the storage solution and by the chemical composition of the binder [with the Ca/Mg ratio being an important parameter (Walkley et al, 2017)], since the absence of calcium in the sodium sulfate solution could favor the formation of hydrotalcite instead of monocarboaluminate due to the decreased Ca/Mg ratio in the outermost surface layer of the flat prism after storage in sodium sulfate solution
Portlandite was found in all hardened binder paste surfaces that were stored in saturated calcium hydroxide solution, but not in the surfaces of samples stored in sodium sulfate solution
Summary
Synthetic dyes are commonly used in textile, cosmetics and other industries. An important group of them are azo dyes in textile industry (Van der Zee et al, 2001). While in most industrialized countries the governmental legislation is becoming more stringent regarding the removal of dyes from textile industry effluents, in most developing and newly industrialized countries, e.g., Pakistan or India, wastewater effluents from textile industry became the main source of pollution of the environment (Kant, 2012; Sarayu and Sandhya, 2012; Imtiazuddin, 2018). With an increased demand for textile products worldwide, there is an increase in production volume of the textile industry and its wastewater proportionally, making it one of the main sources of severe pollution worldwide (Sarayu and Sandhya, 2012). The present contribution would like to contribute to the improvement of this environmental problem
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