# The Use of a Composite of Modified Construction Aggregate and Activated Carbon for the Treatment of Groundwater Contaminated with Heavy Metals and Chlorides

## TL;DR

This paper explores a new composite material for cleaning groundwater contaminated with heavy metals and chlorides, showing high removal efficiencies in lab tests.

## Contribution

The study introduces a modified construction aggregate and activated carbon composite for effective removal of heavy metals and chlorides from groundwater.

## Key findings

- The composite achieved 85% chloride removal and over 79% removal of heavy metals like Pb, Cd, Ni, Cu, and Zn.
- Adsorption followed pseudo-second-order kinetics and fit well with Langmuir, Toth, and Redlich–Peterson isotherm models.
- Modifications to the composite significantly improved its performance in removing contaminant mixtures.

## Abstract

The treatment of contaminants from road infrastructure poses significant challenges due to their variable composition and the high concentrations of chloride ions, heavy metals, and oil-derived substances. Traditional methods for protecting groundwater environments are often insufficient. A promising alternative is permeable reactive barrier (PRB) technology, which utilizes recycled materials and construction waste as reactive components within the treatment zone of the ground. This paper delves into the potential of employing a composite (MIX) consisting of modified construction aggregate (as recycled material) and activated carbon (example of reactive material) to address environmental contamination from a mixture of heavy metals and chloride. The research involved chemical modifications of the road aggregate, activated carbon, and their composite, followed by laboratory tests in glass reactors and non-flow batch tests to evaluate the kinetics and chemical equilibrium of the reactions. The adsorption process was stable and conformed to the pseudo-second-order kinetics and Langmuir, Toth, and Redlich–Peterson isotherm models. Studies using MIX from a heavy metal model solution showed that monolayer adsorption was a key mechanism for removing heavy metals, with strong fits to the Langmuir (R2 > 0.80) and Freundlich models, and optimal efficiencies for Cd and Ni (R2 > 0.90). The best fit, at Cd, Cu, Ni = 0.96, however, was with the Redlich–Peterson isotherm, indicating a mix of physical and chemical adsorption on heterogeneous surfaces. The Toth model was significant for all analytes, fitting Cl and Cd well and Pb and Zn moderately. The modifications made to the composite significantly enhanced its effectiveness in removing the contaminant mixture. The test results demonstrated an average reduction of chloride by 85%, along with substantial removals of heavy metals: lead (Pb) by 90%, cadmium (Cd) by 86%, nickel (Ni) by 85%, copper (Cu) by 81%, and zinc (Zn) by 79%. Further research should focus on the removal of other contaminants and the optimization of magnesium oxide (MgO) dosage.