Metal ion in soil can be immobilized by a process called stabilization. This can be done through a variety of methods including precipitation, ion exchange, adsorption, and encapsulation. Biochar, a charcoal-like substance made from biomass, has been found to be an effective tool for remediating heavy metals in soil. It works by binding to the metal ions, preventing them from leaching into surrounding water sources and making them unavailable for plant uptake. Biochar also increases soil fertility and reduces the toxicity of metals present in the soil.

Biochar amendment is a promising approach to mitigate soil contamination via immobilizing heavy metals and organic pollutants. The quality characteristics of biochar as a soil amendment varied greatly with the feedstock materials and the pyrolysis conditions. Soil-incorporated biochar was able to stabilize Cd, Cu, Ni, Pb, and Zn and reduce their bioavailability through enhanced sorption and chemical precipitation. The stabilization efficacy was largely determined by cation exchange capacity, pH, and ash content of the biochar. Biochar amendment increased the mobility of anionic toxic elements in soil. Soil-incorporated biochar was also able to absorb non-polar organic compounds and polar organic compounds. The adsorption efficiency was controlled by the biochar surface properties specific surface area, microporosity, and hydrophobicity. Biochar may facilitate the mineralization of organic pollutants by enhancing soil microbial activities. The effectiveness of biochar-facilitated soil remediation was case specific, changing with the biochar source, amendment rate, placement, soil type, and pollutant species. Biochar reduces soil density and soil hardening, increases soil aeration and cation-exchange capacity, and changes the soil structure and consistency through the changes in physical and chemical properties. It also helps to reclaim degraded soils.The larger surface area and higher surface energy are helpful for biochars to strongly absorb the heavy metal pollutants and remove them from the soil. Possible mechanisms for the heavy metal retention by chars are the formation of metal (hydr) oxide, carbonate, or phosphate precipitates and/or the activation of surfaces caused by the pH rise, and sorptive interactions between d-electrons of metals and aromatic π-electrons of chars, and specific metal.

There are several methods for immobilizing metal ions in soil, which can help to reduce the risk of contamination and the potential for human and environmental exposure. Some common approaches include:

Physical separation: This involves separating the contaminated soil from the rest of the soil, either by excavation or through the use of physical barriers such as clay or plastic sheeting.

Chemical treatment: This involves adding chemicals to the soil that react with the metal ions and form stable compounds that are less soluble and less mobile. This can be done using chemicals such as lime, sulfur, or phosphate.

Biological treatment: This involves using microorganisms or plants to remove or immobilize the metal ions. For example, certain types of bacteria can bind to metal ions and form insoluble compounds, while certain plants can absorb metal ions through their roots and store them in their tissues.

One type of material that has been shown to be effective at immobilizing metal ions in soil is biochar. Biochar is a type of charcoal that is produced by heating organic matter, such as wood or agricultural waste, in the absence of oxygen. Biochar has a high surface area and a complex pore structure, which makes it highly porous and reactive. When added to soil, biochar can absorb and adsorb metal ions, as well as other contaminants, and help to reduce their mobility and bioavailability. Biochar can also improve soil structure and water-holding capacity, which can further enhance its ability to remediate contaminated soil.

It is important to note that the effectiveness of these methods will depend on the specific characteristics of the soil and the contaminants present, as well as the specific conditions of the site. It is always recommended to seek the advice of a qualified professional before attempting any remediation activities.

Kailash Srivastava

· Retired Patent Examiner for U.S. Government,

· Former Executive Vice President, Technology Commercialization A BIOTECH Company in Northern Virginia, USA

I agree with Peter Donkor that there are a number of methods to remediate soil contaminated with heavy metals or metal ions. Biochar is one of a few options. A multipurpose adsorbent, HUMASORB™ is a better option in my opinion. This is because, HUMASORB™ is available both; as a solid and as a liquid (viz., HUMASORB-CS™, HUMASORB-L™). Thus, it is applicable for a long-term adsorption in form of a solid plaque to separate the contaminated parts from non-contaminated part. As a liquid, the contaminated metal ion will be leached from the soil and will stabilized in-situ. Additionally, HUMASORB™ also adsorbs radionuclides as well as organics (e.g., TCE and PCE). This product has been successfully employed to remove organics including process water from decontamination of obsolete warfare munitions at as site of US military, remediate mine water at a site in Montana, U.S.A., and also some sites contaminated with TCE, PCE and radionuclides. Please see enclosed article. To obtain HUMASORB™ samples, please contact Dr. Daman Walia at [email protected]