Heavy metals (HM) are considered as the most hazardous environmental pollutants because they are prone to cause serious harm in human organisms. Heavy metals enter the human body through the intake of food and water as well as by inhaling dust Many HM accumulate in living organisms over time and pose serious health problems The most dangerous metals to human health are mercury, cadmium, lead, arsenic, copper, tin. and zinc.
The iron and steel, cement and chemical industries are characterized by large volumes of annually produced waste containing HM, radionuclides, and other contaminants. Available information about the levels of certain contaminants in industrial waste is either incomplete or deliberately understated by the metallurgical and cement-producing industries. In order to obtain certificates authorizing the use of silicon-containing waste in agriculture and construction, contaminants must be shown to be low. However, the metal and cement industries take advantage of the shortcomings of Russian legislation with respect to industrial waste disposal Rigorous standards to control the ecological dangers posed by HM waste do not exist.
Metal production cycle.
Metallurgical and cement industries have always produced large amounts of waste because of the technologies they use. The production process entails the extraction of metal from ore. Key stages of this process are ore processing, metal smelting, and then re-melting certain conditions. The first two processes yield the most metallurgical waste. It should be noted that ore contains a large amount of silicon compound. The enrichment and smelting processes involve the separation and extraction of the metal- and silicon-containing substances. The percentage of silicon content in the ore is often higher than the content of the desired metal. As a result, gigantic waste piles accumulate and large dumps of waste arc found at most large metallurgical plants.
As early as 1881 in the United Sates it was suggested for the first time that industrial waste could be used as a silicon fertilizer. Utilization of large amounts of silicon-containing industrial waste was possible by integrating it into the soil to improve fertility and increase plant resistance to adverse weather conditions.8 Another application of the waste was to use it as gravel for road construction.
The history of silicon fertilizers and the use of silicon-containing industrial waste as soil ameliorants can be divided into several time periods. From the early twentieth century to the mid-1950s many studies of silicon concluded that it protected plants from fungal diseases. The experiments were conducted most aggressively in Japan, where empirical data showed the effectiveness of silicon fertilizer and soil ameliorants. As a result, in 1955 a governmental decree requiring the use of silicon fertilizer for growing nee was published in Japan.9 Metallurgical waste products also have been used in Japan.
The period from the mid-1950s to the late 1990s was characterized by theoretical research, which established the impact of active forms of silica on the soil-plant system. At the same time, in some countries (USA, Brazil, Australia) large-scale experiments were conducted on the use of silicon-containing wastes in agriculture Since 2000, a sharp increase has been seen in the use of silicon fertilizers. This can be explained by the accumulation of knowledge regarding the positive effect of silicon on the soil-plant system, as well as by a new appreciation for traditional fertilizers and crop-protecting chemicals. The use of silicon-containing compounds in plant growing allows the reduction of the doses of conventional fertilizers and pesticides and at the same time increase the yield of crops.
Therefore, silicon fertilizers found in industrial waste have been used much more intensively in recent years. As a result, today more than 7 million tons of metallurgical waste is recycled world-wide. Continued growth of the use of silicon-containing compounds in agriculture is expected, in particular with regard to the effects of climate change. The optimal silicon plant nutrition increases the resistance of agricultural crops to moisture deficit and excess salt in the soil.
One of the purposes of our research was to evaluate the content of HM in w aste as one of the key components posing risks to the environment and human health. Initially, we undertook a study of metal and cement industry waste to evaluate the possibility of using some of this waste as fertilizers and soil silicon ameliorants.11 Three ways for obtaining the samples of industrial by-products were used: a) samples obtained from factory waste on site, b) samples sent to the author from other factories, and special exhibitions and c) samples of metallurgical and cement industries’ waste collected in dozens of plants in various regions of Russia over the course of three decades, from 1984 to 2010.
An examination of the waste samples identified the total amount of HM in accordance with standard methodology’,12 the X-ray fluorescence method to analyze solid samples,13 and the atomic adsorption method with an alkaline sintering and subsequent dissolution of solid samples.14 Analysis of waste by the X-ray fluorescence method w as performed in the geology department of Moscow State University during the years 1986-1990. The analysis of waste using the atomic-adsorption method was performed at the Institute of Physical, Chemical and Biological Problems of Soil Sciences, Russian Academy of Sciences, between 1991 and 2010 All analyses were performed in three-stage replication.