Soil scientists use mining waste to restore manmade wasteland
Soil scientists and chemists from RUDN University, together with colleagues from the Kola Science Center of the Russian Academy of Sciences, have developed and tested a method of ecosystem restoration in the sub-Arctic technogenic wasteland contaminated by the waste of non-ferrous metallurgy enterprises. The technology is based on the use of mining waste capable of neutralizing toxic metal compounds for plants. The study involved scientists from different fields of natural sciences—geochemistry, soil science, microbiology and ecology. The article is published in the journal International Soil and Water Conservation Research.
Industrial processing of ore and smelting of non-ferrous metals leads to contamination of the soil with copper, nickel, zinc and lead. In high concentrations, these are dangerous for humans and the environment. Heavily contaminated soils lose fertility, and vegetation and soil biota are killed and degraded. As a result, water and wind erosion increases and such regions become human-made wastelands. The world's largest human-made wastelands are located in the Russian Arctic, where large deposits of non-ferrous metals and metallurgical enterprises are located; these northern environments are extremely sensitive to anthropogenic influences.
A field experiment on the use of alkaline mining waste for the restoration of human-made wastelands in the Murmansk region was started by scientists from the Kola Science Center. A few years later, in 2010, it was continued by soil scientists of RUDN University.
On the site of the wasteland, located 1.5 kilometers from the plant for processing sulfide copper-nickel ores, scientists have created technosols consisting of two layers: the upper layer is hydroponic vermiculite, which is able to retain moisture and promote plant growth; the lower consists of waste containing carbonates and silicates of calcium and magnesium. Nearby control areas were created without adding a layer of waste, and the plants died during the first year of the experiment because of the high toxicity of the soil.
On each site, the researchers sowed a mixture of seeds of perennial grasses growing in northern conditions—red fescue (Festuca rubra L.), meadow fescue (F. pratensis Huds), awnless rump (Bromus inermis Leyss) and emerald festulolium (X Festulolium F. Aschers. et Graebn). Complex fertilizers containing nitrogen (16 percent), phosphorus (7 percent) and potassium (13 percent) were introduced into the soil once a year (except for the last year of the experiment).
Seven years after the creation of tecnhosols and seeding grass, the researchers assessed indicators of efficiency of technologies for the remediation of wasteland: indicators of soil succession, state of vegetation cover, and accumulation of metals in vegetation and soil component of ecosystems.
After getting the results of this experiment, the researchers assessed the quality of the soil and the condition of the plants: the height of the grass, above-ground biomass, metal content accumulated in technosols and plants as a result of emissions of metallurgic plant and also the organic carbon content, humic and fulvic acids, the content of carbon of microbial biomass and activity of soil microorganisms. Further, the results were compared with data on waste and soil characteristics of the original technogenic wasteland.
The results of the study showed that despite the constant atmospheric deposition of heavy metals, an active soil-forming process takes place at sites with technosols based on mining waste. They accumulate organic carbon, and the content of organic substances and microbial biomass after seven years of development of technosols were comparable to the parameters of natural soils.
The maximum biomass of grass cover was in the variant with the use of waste containing serpentine minerals in its composition, which is due to the high content of silicon available to plants in the waste, which is a factor of stability of cereal plants under stress.
"Natural restoration of disturbed ecosystems in Arctic conditions takes at least 30 to 35 years. In conditions of extreme degradation of soil and vegetation on human-made wastelands, this process can take hundreds of years. The results of the experiment show that the use of mining waste as a component of artificial soils—technosols—allows not only to prevent soil erosion and create vegetation cover in the conditions of constantly occurring emissions of metals, but also to accelerate the recovery of soils and reduce the migration of heavy metals into the environment," Viacheslav Vasenov said.
According to Vasenov, about 100 square meters of the territory has been reclaimed so far using the new method, and 10 types of mining waste were used in the experiments.
"Today, this method is optimal in terms of labor costs and economic efficiency, because the technology is based on waste from mining enterprises, that is, materials with low cost," the researcher concluded.