The Role of Soil Washing in Contaminated Land Remediation

What is soil washing? Soil washing is a technique for the clean-up of land which has become contaminated with hazardous substances. The purpose of the land clean-up is to make it safe for future use, such as development for homes.

Main Concept and Description of Soil Washing

The technology is a process which uses liquids (usually water, but on occasions, the water is combined with chemical additives) and a physical process which engineers liken to scrubbing, but what are scrubbed are soils (to you and me “dirt”). By carrying out this so-called “scrubbing” they remove the hazardous contaminants. They collect them and concentrate them so that they are in a much-reduced volume. This means that the reduced volume can be neutralised in a further process, at a much-reduced cost, because the volume is far less.

The whole process is based on a remarkable fact. The common fact about hazardous contaminants is that they tend to bind (get stuck in), chemically or physically, to silt and clay. Silt and clay, in their turn, also get stuck on/ or against sand and gravel particles. So, once the soil washing process has separated the contaminated fine soil (silt and clay) from the coarse soil (sand and gravel), the smaller volume of soil now comprises the majority of the fine silt and clay particles. Thes are further treated by using other techniques (such as incineration or bioremediation) or disposed of responsibly via incineration or sometimes to landfill. The precise route is strongly influenced by regulations designed to protect people’s health against the hazardous chemicals involved. naturally all chemical use id subject to state and federal regulations. The clean, larger volume of soil is not toxic and can be used as backfill often on the same site as they originated with obvious cost savings and environmental benefits.

The Problem Soil Washing Can Solve

There is an urgent need to release land in industrial cities. That means that developers need to be able to decontaminate the soil in development zones. The demand for soil remediation on contaminated land also has dramatically increased in recent years. Research has been done which has raised expertise on the subject which has led to methods have been found to remove the well-known hazardous substances (both organic contaminants and metals), and also more recently found pollutants. The new technology should help to provide more land for homes and industry to meet an ever-increasing demand for homes close to the jobs people need. Brownfield sites and metal-polluted old industrial locations are significantly being made use of as places for redevelopment.

The danger of pollutants seeping right into water resources can result in the loss of aquifers which would otherwise provide much-needed drinking water without expensive water treatment. The WHO provides a guide on the installation of decontamination systems. This can remove the problem of polluted soils which are resulting in bioaccumulation of chemicals in pets and farm animals which can ultimately get into the food chain. This waste of natural resources is scandalous and must be avoided. Solutions must be found. Eliminating contaminants and impurities in the dirt is vital to ensure food security for both humans and wild animals.

Liao et al. (2016) have published a research report on soils processing which demonstrates that for porous sandy soils with high permeability the soil washing method is suitable. Once the soil has a high content of organic matter or clays (30%), soil washing is considered ineffective for heavy metal contaminant remediation by researchers. However, the soil particles finer than 0. 02 mm can be washed but only if the contaminants can be solubilized by using suitable reagents such as chelating agents to create sludge.

Ex-Situ Physical/Chemical Treatment

Single-factor experiments where just one parameter is changed each time are used to painstakingly investigate the remediation effect of single and mixed washing of hazardous arsenic-contaminated soil. The same method of washing soil can be done for certain heavy metals. The optimal washing conditions, washing kinetics and speciation distribution of arsenic have been determined. The obtained removal efficiencies of arsenic in the soil is 83. 65%, which could be remedied to less than “ risk intervention values (as < 140="" mg·kg−1)="" for="" soil="" contamination="" of="" development="" land="">

The process removes hazardous polluting contaminants from soils by soil washing soil extraction in one of the following 2 ways:

• By suspending or dissolving them in the wash water itself (by careful control of the pH for a period of time); or
• By getting them together in a more concentrated smaller volume them into a smaller volume of soil. This is done by particle size separation, gravity separation, and attrition scrubbing (which might sound complicated but in reality has been done for many years by sand and gravel quarry companies).

By applying these techniques to projects in a rigorous and quality control manner by responsible contractors applying standards applied by bodies such as the United States EPA, large areas of derelict land can be brought back into use. As this land is close to cities and the jobs people need to sustain their lifestyles, the benefits of these weird-sounding techniques for so-called “soil washing” and other similarly applied technologies can be effective with immense benefits.

 

 

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