Friday, 10 April 2015

Heavy Metal

I'm sure many of you have read about the effect mine spoil has on vegetation and the difficulty that some plants have in colonising spoil heaps. I've always enjoyed walking on spoil heaps as the plants that do manage to colonise are often rather scarce or not found in the surrounding countryside.  My local heap is the site of the old Gedling Colliery although Nottinghamshire is dotted with many similar sites and all of them if they haven't been capped by clay still show traces of mine spoil. The majority of Gedling has been capped but those areas still uncapped are pretty good floristically.  One of the major waste products discarded from coal mining are nodules of iron pyrites commonly known as fools gold, chemically Iron Sulphide. Iron pyrites occurs commonly in the carboniferous measures of Nottinghamshire and can be found on the spoil heaps if you keep a keen eye out.  I picked one such nodule up several years ago and brought it back to my garden and plonked it onto my rockery. This rockery is covered by Helxine soleirolii, "baby's tears" that creeps over and around the stones. As can be seen after a wet and damp winter it struggles where the Iron pyrites sits, in summer it manages to grow around and below the pyrites lump.  The reason for the dieback is the reaction between pyrites air and water,  the resultant products form both Iron oxides and Sulphuric acid. It's the sulphuric acid run off that's causing plant death.   I think the picture illustrates it rather well.

 Helxine damage caused by Iron pyrites derived sulphuric acid (10p for scale)

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