Potential impact of dispersion products of magnetite quartzites on the environment

Abstract

Using XRF, TG-DTA, chemical and sedimentation analysis of the products of processing of magnetite quartzites from the N Ore Processing Plant of Krivorozhye, changes in the phase and chemical composition of samples of four stages of magnetic separation and tailings were traced compared to a sample of the raw ore, and the potential impact of the dispersion process on the environment was revealed. Thermogravimetric studies indicate phase transformations of magnetite to maghemite (250-340 ° C), polymorphic transformations of iron oxides and destruction of rock-forming minerals (430-480 ° C), conversion of alpha quartz to beta-form (564-568 ° C), dehydroxylation of iron and magnesium oxyhydroxides (385 ° C), conversion of beta-quartz to beta-cristobalite (970 ° C). In the process of enrichment, there is an increase in the loss of mass of the samples, which is %: 0.06 (I); 1.46 (II); 1.9 (III), and 2.6 (IV). According to X-ray diffraction, the main ore mineral is magnetite, the rock-forming mineral is quartz. Among the secondary minerals are sulfides, cummingtonite, actinolite, and others. It is shown that at the first stage of enrichment all primary and secondary minerals are present in the samples, at the 2nd stage sulfides disappear from the sample, at the 3rd stage secondary minerals disappear, and at the 4th stage quartz remains in the sample and it forms aggregates with magnetite. The parameter of the crystal lattice of magnetite varies between 8.397-8.403 nm, its coherent scattering region (CSR) is 31.4-35.6 nm. It is found that in the course of ore grinding the destruction of secondary minerals takes place with the removal of destruction products, as evidenced by the occurrence of disperse quartz in the tailings. According to sedimentation analysis data, in the first 20 seconds, more than half of the particles with a size of 24-28 μm were deposited from the pulp, after 3 minutes, particles with a size of 8-9 μm settled, after 6 minutes - particles with a size of 6-7 μm. Within 30 minutes, almost complete precipitation of particles with sizes of 4.5-2.7 μm was observed. Hydraulic classification of the tailings showed the deposition of mainly quartz particles in the first and second chambers of the separator, actinolite and muscovite particles were separated in the third chamber, and cummingtonite, biotite and chlorite in the fourth chamber. Analysis of the chemical composition of the dispersion products indicates that Si, Ca, and Na accumulate in the tailings, whereas Ti is removed, and could potentially enter the environment. It is shown that the tailings and separation products increase the content of Zn, and the tailings accumulate environmentally hazardous As, and Nb. At the same time, the concentrations of other elements remain stable at all stages of processing.