Dear Fredrick,

- If the HM are the major cations in solution, an attenuation process can be the cation exchange (provided by, e.g., clay minerals). A complete data studio about natural clays which represent a barrier to the migration of leachate contaminants is “Regadío et al. Pollution profiles and physicochemical parameters in old uncontrolled landfills. Waste Manag 2012;32:482–97”.

- Basic conditions provided by, e.g., calcite (carbonate minerals), keep the HM precipitated in forms such as of S2-, O2-, OH-, CO32- :

(1)Bellir et al., 2005. Study of the retention of heavy metals by natural material used as liners in landfills. Desalination 185, 111–119

(2) Mostbauer, P., 2003. Criteria selection for landfills: do we need a limitation on inorganic total content. Waste Management 23, 547–554).

In addition, it was seen that Cr, Cu are incorporated into crystal lattices of calcite.

Acidity should be avoided because of the dissolution of minerals (e.g., calcite) and mobilization of metals. The former would decrease the soil density, increase its porosity and, consequently, the hydraulic conductivity; which would release HM dissolved in the porewater and reduce the retention capacity of the substratum:

(1)Wong CSC, Wu SC, Duzgoren-Aydin NS, Aydin A, Wong MH. Trace metal contamination of sediments in an e-waste processing village in China. Environ Pollut 2007;145:434–42

(2) M. Regadío et al. 2013. Processes and impacts of acid discharges on a natural substratum under a landfill. Science of the Total Environment 463–464 (2013) 1049–1059

 If not possible, it could be used CaCO3 as an amendment.

Hope it helps.

Depending on what the soil is to be used for, a number of remediation processes subsist. Perhaps the fastest is to strip off the affected layers. Following years of devastating consequences of dioxins on the Vietnamese soil, the affected soils were recently stripped and subjected  to high temperature. The links provided hereunder may prove useful.

http://www.epa.gov/superfund/remedytech/tsp/download/issue14.pdf

http://www.geology.gov.yk.ca/pdf/mperg_2000_6.pdf

FredricK,  we hope you could be specific.  What kind of soil and what kind of metal?  Otherwise, the answers will be different.  Depends.

Dear Yue,

Thanks for your response.

The soil is a loamy-clay soil (25:75) and the metals are pb and Zn.

Kind regards,

Fred.

Fredrick,  I see 2 ways to fix the problem in addition to soil excavation to remove the impacted soil:

1. Fixation of the soil with concrete.  The metals will be fixed in place (in soil).

2. in-situ oxidation or precipitation by chemicals that react with pb and Zn.

Depends on which soil properties are affected by HM. First you need to work on soil pH adding calcarous material, Pb and Zn are known to be stable in soil at pH over 6,5. Important issue is if  those HM are found as mobile forms in soil not as much in total concentration.  Mobile forms tends to be translocated in plants. If you choose hyperaccumulators to remove HM you need to increase the bioaccesibility, that mean mobile forms of HM. There are various methods like stabilization/solidification knowns as S/S, you can use zeolites (will extract HM and replace its with Ca, K because are rich on it). 

attenuation by RENA in environmental remediation is recommended such that natural processes of oxidation and reduction following soil chemistry principle will be applied where these metals will be precipitated and removed.

There will be addition of certain friendly materials to aid the attenuation processes check some of such recommended by colleagues above.

in each of the processes, the pH which is central  is stabilized 

Dear Fredrick,

You still need to be a little more specific. What is the level of the contamination, what level is acceptable, size of the site, soil intended final use....is it for agricultural purpose,  for a park, a residential area, runs off into a waterbody, etc?

There are a number of options ranging from physical (engineering) to chemical (chemical amendment), to biological (bioremediation, biosolids amendment) methods, and combinations of these.

The rule of them is to slow down the solubility of HM with the addition some amendments like Mono-Amonium phosphate, Ca-sources like gypsum etc or organic matter. On the other hand, use some materials those enhance the availability of  HM with the application amendments like acids, acid formers, EDTA etc followed by growing high biomass producing crops those are nt directly consumed by the humen beings.

The rule of them is to slow down the solubility of HM with the addition some amendments like Mono-Amonium phosphate, Ca-sources like gypsum etc or organic matter. On the other hand, use some materials those enhance the availability of  HM with the application amendments like acids, acid formers, EDTA etc followed by growing high biomass producing crops those are nt directly consumed by the humen beings. Even introduction some ionic spp to the system to promote competition for metal absorption by plants could do the needful, e.g. Cd, Pb and other divalent HM could be attenuated with the addition of Ca.

in general, you have physical and chemical means, depending upon what kind of metals, and physical characters, or chemical characters.  Can you be specific?

There is also an interaction between grain size distribution (but also which minerals are present) of the soil and the specific solubility  of the metal compound. To describe the characteristics of a metal-contaminated soil, it is useful to determine the leachability of the relevant metals for each particle size fraction. I have investigated soils from chlorine plants and acetaldehyde factories (main contamination Hg) for various plants all over the world and it was interesting to see how different soils from industrial remediation can be. This was done under an engineering perspective with regard to treatment particularly soil washing.