Effect of amendments made of waste materials in the physical and chemical recovery of mine soil

• A copper mine soil was treated with two amendments made of different wastes.
• The physico-chemical degradation of the untreated mine soil was considerable.
• Wastes can increase the concentration of C and N in degraded soils.
• The evaluation of wastes is important when before being used as amendments.

The process of obtaining minerals required by society entails a series of impacts caused by mining. In order to minimise these impacts, amendments have now been used for several years made of waste material in order to recover mine soils. Two amendments were used in this experiment: A1 (a mixture of sludges from a bleach plant, urban solid waste and material from the area around the mine) and A2 (sludge from a purification plant, wood chips and remnants from agri-food industries). These amendments can improve the characteristics of the mine soils by increasing their pH and concentrations of carbon and nutrients, as well as reducing the concentration of metals in bioavailable form. However, the use of wastes can add metals to soils; so it is important to control their concentrations before being used. With the aim of knowing how these amendments perform over time, an experiment was carried out in plant pots, amending a soil from the settling pool from a former copper mine located in Touro, in north western Spain. The pseudo-total and DTPA-extractable concentration of metals, nutrients in phytoavailable form and pH of the soil were measured over a 3-month period. At the end of the experiment, it was found that both amendments caused in increase in the pH and concentrations of basic cations, carbon, and humic and fulvic acids. The amendment made of solid urban waste (SUW) caused an increase in the concentration of DTPA-extractable Pb and Zn. For these reasons, when applying these amendments it is important to take into account to which types of soils they can be applied. To amend this mine soil, the materials used in the amendments A1 and A2 would be valid, as the soil from the pool is already contaminated by metals and cannot be used for agricultural purposes.