Environmental Aspects of Phosphate and Potash Mining

Environmental Aspects of Phosphate and Potash MiningCapping Salt Tailings Pile with Demolition RubbleThe Kali und Salz GmbH former Frederickshall operationis located near Hannover in northwest Germany.The relatively small salt tailings pile, containing 11 milliontonnes of salt and kieserite, closed in 1978.Rehabilitation of the pile by capping with demolitionrubble, commenced in 1997, using a patented method.Capping is conducted using inert demolition rubblefrom the city of Hannover, 25 kilometres away. The rubbleis delivered to a waste management station locatedadjacent to the stack where it is weighed and visuallyinspected. Sampling occurs at regular intervals to checkfor potential contaminants that could present an environmentalhazard. Any metal is removed and the rubbleis crushed and sorted by coarseness. A portion of theaggregate is suitable for resale to be used in new civilconstruction activities.Capping of the salt tailings pile is conducted by placingthe coarse fraction adjacent to the salt to create a capillarybreak and drainage layer followed by theplacement of the fine fraction on the outside. The cappingis designed to leave a stable final slope andrequires the placement of material in a layer from 1 to30 metres thick. After capping is completed, a 3 metrethick layer of soil will be placed on the outside as agrowing medium for revegetation.The rate of capping is limited by the supply of demolitionrubble. At current levels of supply the capping isexpected to be completed in 30 years. Monitoring of thecapped areas has indicated that capillary action isaffecting only the first 10 to 20 centimetres of overlyingmaterial.This capping method appears to provide an effectivemeans of isolating salt tailings from the external environment.Additional benefits arise from the recovery offormerly landfilled urban waste for use as both a saltstack capping material and a raw material for new construction.This extends the life of the city's landfill.Sorting and crushing demolition rubble - Kali und SalzGmbH, GermanyPlacing rubble against salt pile - Kali und Salz GmbH,Germanyto quickly stabilize the surface and allow the establishmentand succession of other slower growing species.Topsoil cover provides a suitable growing medium onthe tailings.A number of companies have conducted trials todetermine the viability of sealing the surface of potashsalt tailings piles, to isolate the salt from the environment,allow vegetation to be established and leave astable landform. Typically, techniques employed usean impermeable layer to isolate the salt tailings fromthe environment, followed by placement of a growingmedium above. The impermeable sealing layer isimportant to prevent water percolating through anddissolving the salt, leading to the loss of foundationsand collapse of the sealing layer and growing medium.A variety of sealing layers have been used including:coarse aggregates to prevent capillary action drawingthe salt upwards to the surface and impermeable barrierssuch as a plastic liner, bitumen, or cement.The growing medium is placed on top of the sealinglayer to allow revegetation and prevent erosion. Insome instances temporary stabilization techniques,such as geofabric, may be applied until the vegetationhas established.Conversion of the post-mining land use to agricultureor other purposes would require trials to select speciesbest suited to the environment and growing medium.