Sustainable tannin-based coagulants synthesized through Mannich reaction using melamine as an amine source for water treatment applications

Adedayo Bello,Tiina Leiviskä

doi:10.1016/j.indcrop.2021.114336

Abstract

This study explored the potential of melamine, as the nitrogenating source for the cationization of pulverized quebracho and spruce tannins. The influence of modification conditions on the properties of the coagulants was studied by varying the formaldehyde and melamine ratios with different activation times and temperatures. Based on considerations of charge density and shelf life, the most viable modifications were established as coagulants synthesized with a 1:0.52 formaldehyde to melamine molar ratio at 70 °C. At optimal conditions, the charge density of the quebracho and spruce coagulants was 2.22 meq/g and 1.04 meq/g, respectively, and the residual formaldehyde content in the coagulants was low. The developed synthesis of this study demonstrated a clear advantage over previous methods due to the rapid modification step. X-ray photoelectron spectroscopy (XPS) confirmed the emergence of an amine which signifies a successful Mannich reaction in the coagulant. Although optimal modification conditions for the coagulants were established at 70 °C (5-min activation time), the average molecular weight could not be determined for these conditions. Nevertheless, electrospray ionization mass spectrometry (ESI-MS) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry measurements revealed that the tannin-based coagulants obtained at lower temperatures (23 °C and 45 °C) possessed low average molecular weight (approx. 800–900 Da). Furthermore, ESI-MS and MALDI-TOF spectra showed that the Mannich modification resulted in the depolymerisation of the quebracho tannin, leading to a reduction in units of higher mass fractions in the synthesized coagulant, which contrasted with the spruce tannin. Jar test experiments with surface and industrial process waters demonstrated that the tannin coagulants enhanced particle settling effectively.

Highlights

Water is a key commodity for many industrial processes, and one main concern is the remediation of industrial effluents, which are usu ally characterised by high turbidity
A visible charge density progression could be observed as the activation time and melamine dosage increased in most Quebracho (Schinopsis balansae) tannin (QT) modifications (Fig. 1a)
This study has shown that melamine can be used as a nitrogenating agent during the aminomethylation of tannins

Summary

Introduction

Water is a key commodity for many industrial processes, and one main concern is the remediation of industrial effluents, which are usu ally characterised by high turbidity. Waters with elevated turbidity induced mostly by the presence of colloids and suspended solids cannot be released directly into the environment without pre-treatment. This concern has been further exacerbated by the changing and more strin gent water quality standards that individual point source dischargers such as industrial facilities need to comply with. Coagulationflocculation is considered the most efficient pre-treatment technique for turbidity removal (Daifa et al, 2019; Teh et al, 2016). The effi ciency of the coagulation-flocculation is dictated by several factors, which include coagulant type and dosage, pH, concentration of organic matter and dissolved solids, ionic strength and temperature of the effluent (Zhu et al, 2011; Sher et al, 2013)

Methods

Results

Conclusion