Abstract
The modified tannin by Mannich reaction was investigated for wastewater treatment. The removal of heavy metals, such as copper, chromium and mercury, in industrial wastewater was evaluated through the coagulation–flocculation technique, using modified Acacia tannin (MAT) as a coagulant agent. The successful tannin modification was evaluated by infrared spectopometry (FTIR), nuclear magnetic resonance (NMR); monitoring the removal of heavy metals was performed by atomic absorption (AA) and a direct mercury analyzer (DMA). Additionally, the parameters of water quality, total suspended solids (TSS), turbidity and chemical oxygen demand (COD) were assessed. Different doses of MAT were evaluated (375 ppm, 750 ppm, 1250 ppm and 1625 ppm) and three different levels of pH (4, 7 and 10). The highest percentages of removal obtained were copper 60%, chromium 87%, mercury 50%–80%, COD 88%, TSS 86% and turbidity 94%, which were achieved with the dose of 375 ppm of MAT at pH 10. The coagulation–flocculation process with the modified Acacia tannin is efficient for the removal of conventional parameters and for a significant removal of the metals studied.
Highlights
Heavy metals are water pollutants that generate a negative impact in the world because they are harmful in high or even low concentrations for humans and animals
The small shoulder at 1720 cm−1 is associated with the C–N link due to the ammonium chloride incorporated into the synthesis of modified Acacia tannin (MAT) [14]
The weak band observed around 1477 cm−1 is related to the aromatic rings stretching vibration that is absent in MAT [18]
Summary
Heavy metals are water pollutants that generate a negative impact in the world because they are harmful in high or even low concentrations for humans and animals. Diseases that led to the search for efficient techniques for the removal of these metals from water. Coagulation consists of the elimination of the double electric layer that the colloidal particles have suspended in an aqueous medium and the flocculation is the process by which the particles previously destabilized in the coagulation are agglomerated [3]; these processes are widely used due to their low cost, speed and efficiency. The most commonly used coagulants are inorganic metal salts, such as aluminum sulfate, ferric chloride and synthetic polymers. The second is that substances such as inorganic salts leave traces of ferric and
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