Monitoring of copper adsorption on biochar using spectral induced polarization method.

Copper contaminant generated from mining and industrial smelting poses potential risks to human health. Biochar, as a low-energy and cost-effective biomaterial, holds value in Cu remediation. Spectral Induced Polarization (SIP) technique is employed in this study to monitor the Cu remediation processes of by biochar in column experiments. Cation exchange at low Cu2+ concentrations and surface complexation at high Cu2+ concentrations are identified as the major mechanisms for copper retention on biochar. The normalized chargeability (mn) from SIP signals linearly decreased (R2 = 0.776) with copper retention under 60 mg/L Cu influent; while mn linearly increases (R2 = 0.907, 0.852) under high 300 and 700 mg/L Cu influents. The characteristic polarizing unit sizes (primarily the pores adsorbing Cu2+) calculated from Schwartz equation match well with experimental results by mercury intrusion porosimetry (MIP). It is revealed that Cu2+ was driven to small pores (∼3 µm) given high concentration gradient (influent Cu2+ concentration of 700 mg/L). Comparing to activated carbon, biochar is identified as an ideal adsorbent for Cu remediation, given its high adsorption capacity, cost-effectiveness, carbon-sink ability, and high sensitivity to SIP responses - the latter facilitates its performance assessment.

The physicochemical interacting mechanisms and real-time spectral induced polarization monitoring of lead remediation by an aeolian soil.

Compared to traditional lead-remediating materials, natural-occurring paleosol is ubiquitous and could be a promising alternative due to its rich content in calcite, a substance known for its lead-removal ability via carbonate dissolution-PbCO3 precipitation process. Yet, the capability of paleosol to remediate aqueous solutions polluted with heavy metals, lead included, has rarely been assessed. To fill this gap, a series of column permeation experiments with influent Pb2+ concentrations of 2000, 200, and 20 mg/L were conducted and monitored by the spectral induced polarization technique. Meanwhile, the SEM-EDS, XRD, XPS, FTIR and MIP tests were carried out to unveil the underlying remediation mechanisms. The Pb-retention capacity of paleosol was 1.03 mmol/g. The increasing abundance of Pb in the newly-formed crystals was confirmed to be PbCO3 by XRD, SEM-EDS and XPS. Concurrently, after Pb2+ permeation, the decreasing calcite content in paleosol sample from XRD test, and the appearance of Ca2+ in the effluent confirmed that the dissolution of CaCO3 followed by the precipitation of PbCO3 was the major mechanism. The accumulated Pb (i.e., the diminished Ca) in paleosol was inversely proportional (R2 >0.82) to the normalized chargeability (mn), an SIP parameter denoting the quantity of polarizable units (primarily calcite).