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Published in CIWM Journal October 2016: Heavy metal or hard rock – both sound good to us!
What do you think of heavy metal and hard rock? Do you have a problem with either or perhaps both? Don’t worry, you haven’t slipped into the pages of Kerrang! magazine; we’re talking soil contamination, not loud music. Peter Hayes, Business Development Executive from waste management specialists, CDEnviro explains more about the issues and emerging solutions.
Over 200 years of industrialisation have caused soil contamination to be a widespread issue across Europe, with heavy metals one of the most frequent pollutants. Land is legally determined to be contaminated when substances it contains could cause ‘significant harm to people or protected species’ or ‘significant pollution of surface waters or groundwater’.
Contaminated soil is a particular problem when trying to bring brownfield sites back into use. So decontamination is important to our economy as well as our environment. Polluted soil can be the result of spillages, mismanaged industrial sites, or unforeseen consequences of using materials previously thought to be benign.
The troublesome twosome
When attempting to process soil, the two largest areas of concern are usually hard rock and heavy metals. Hard rock can be big, abrasive and difficult to process and really takes its toll on machinery. Heavy metals, such as cadmium, lead, chromium, copper and zinc – either on the soil or at elevated levels within it – can result in problems with processing and therefore high disposal costs of waste materials.
Although there are solutions on the market, the problems of hard rock and heavy metals don’t usually exist in isolation and the options for dealing with them simultaneously are extremely limited. Machines for dealing with hard rock require a great deal of force, but a more finessed approach is needed when dealing with the heavy metals. However, it is costly and time consuming to deal with them separately.
What’s the problem?
Site contamination is unique in each case, and is dependent on the legacy of what has happened on the land before remediation was required. Although heavy metals are naturally present in soil, any more than trace amounts are detrimental. Although the health effects are less well studied than air and water pollution, there is a growing body of evidence of the dangers of contaminated soil. Contamination can affect human health either through direct contact or by ingestion through the food chain. There is also the risk of inhalation to consider including anthrax spores, small pox and noxious gases.
Contamination comes from a variety of sources: mostly industry (non-ferrous industries, but also power plants and iron, steel and chemical industries). A site-by-site approach to assessing risk is needed. This must take into account the individual environmental characteristics of soils and human activities that have taken place there or nearby. Each site has a unique risk profile, chemistry and history. Therefore a flexible approach to decontamination is required. A customised approach is needed at every site.
Dealing with the problem
In the European Union, the treatment of waste is regulated by a number of directives, which define the scope and stipulate general rules for the treatment of waste containing heavy metals. The aim is to increase the recycling rates of these materials by regulating the treatment of composite waste products, such as electronics, vehicles and batteries. A number of directives now regulate the content levels of the heavy metals cadmium, mercury and lead in marketed products in order to reduce their use.
Landfills across Europe are increasingly reluctant to accept these waste materials. Many countries are now using tax receipts and revenues generated from environmental levies to reclaim contaminated sites to create a positive legacy for this land. Forward thinking EU countries reinvent landfill revenues into remediation projects, however appropriate recycling centres are rare and incur significant transport across international borders.
There are ‘big bruiser’ machines that are able to deal with large stones, but they are not equipped to deal with the chemical side of the problem. Likewise where scientists have come up with a solution for the heavy metals, the machines all too often fall down due to wear and lack of robustness when dealing with the larger stones.
However, there are companies, like my own, which have identified this issue and developed a middle ground. We bring science and engineering together to provide a solution to brownfield remediation which finally bridges the gap between the theoretical and the practical. It’s safe to say we like the sound of heavy metal and hard rock!
How does it work?
Our approach is to customise a design for the likely contaminants, the space available, and the degree of modularity/portability required. Often these systems are designed to be modular, portable systems to move from site to site, or they can be fixed turnkey installations. This gives the flexibility required whatever the location and contaminant.
When dealing with heavy metals, we can bring material scrubbing and recovery processes into play, and then tertiary water treatment to allow us to reuse water that becomes heavily contaminated in the recovery process.
Hydrocarbons can also be removed from the surface of the contaminants and then isolated and removed from the washing water afterwards. Alternative soil remediation processes use chemicals like surfactants. However, an efficient mechanical washing and scrubbing process really reduces the need for this, or even eliminates it entirely, which brings a huge saving on operating costs. The machines can also deal with organic matter, and enable clean stones to be reused within construction.
So now the choice is no longer between hard rock and heavy metal, they can be mixed together, which should be music to anyone’s ears!