Hydrotalcite-Based Porous Concrete Filter for Lead Removal from Wastewater

This study explores the effects of synthetic hydrotalcite (Mg-Al layered double hydroxide, i.e., Mg-Al LDH) in an ordinary portland cement–based porous concrete on (1) improvements in mechanical properties, (2) water permeability through the concrete, and (3) its use as a filter on Pb(II) removal and its reusability. Two systems were studied: (1) LDH-incorporated concrete (LIC) filters, utilizing 2% hydrotalcite as a binder [Ordinary Portland Cement (OPC)] replacement, and (2) LDH-coated concrete (LCC), where fine aggregates were coated with 2% hydrotalcite. LDH-incorporated concrete, in particular, showed a significant increase in compressive strength (approximately 39%) and split tensile strength (approximately 10.3%) compared to control concrete, while retaining similar permeability. Hydrotalcite LDH-modified porous concrete was found to be highly effective in removing Pb(II) from water. Batch studies revealed that both the LIC and LCC systems followed pseudo-second-order kinetics in Pb(II) removal. The observed equilibrium results for both LIC and LCC systems followed the Langmuir isotherm model, with good adsorption capacities of 23.42 and 18.14 mg/g, respectively. Subsequently, the performance of the LIC system was compared under continuous operation under two modes: (1) as a cast, rigid column, and (2) a packed bed of crushed aggregates of size 1–2 mm, simulating the use of construction debris. After 8 h of continuous operation with a feed containing 15 ppm of Pb(II), the packed bed showed superior Pb(II) removal of 99.0% compared to the rigid column (97.3%). Effects of coexisting ions and pH were studied for the LIC system. These preliminary results validate the possibility of a low-cost LDH-based porous concrete to serve as an effective pavement material, as well as a capable adsorbent, even in its debris form, for Pb(II) metal removal from waste/storm water.