RECYCLING OF AURIFEROUS ORE FLOTATION TAILINGS IN SLAG-ALKALINE CEMENT

Research analysis aimed at stabilizing processes in industrial waste and other, similar hazardous ion containing materials, shows that these materials can be successfully stabilized, if they are bound as a mineral component in cement. Considering that auriferous ore flotation waste contains heavy metals that are useless for any production and accumulated in dumps, storages and sumps, this impairs the ecology of the country. This is why current study is conducted on recycling of auriferous ore flotation tailings by binding it as a cement component, which is also can be one of its effective applications. For heavy metal bonds stability evaluation in the composition of the cement matrix, the method of leaching elements by atomic spectroscopy was applied. According to the research it was found that application of slag-alkaline viscid systems for recycling of auriferous ore dump flotation tailings provides considerable advantages over traditional Portland cement systems based on PC I-500. It was shown that along with the physical blocking in the artificial stone matrix, based on slag-alkaline viscid systems, elements of heavy metals were also bound chemically as a part of structure-forming compounds. In this regard use of auriferous ore dump flotation tailings (10...30 %) in the compound of slag-alkaline cement results in the prolonged solidification and provides the same level of cement stone durability as the check sample compound.


Introduction
Thorough studies in the field of construction materials science allow conducting a rational disposal of technological waste, for which one of the main sources is mining industry.Through the use of secondary material resources it is possible to solve a number of important tasks such as saving raw materials, preventing water, soil and air pollution, reduction of energy consumption in construction materials production.However, despite the environmental hazard of mining industry waste, annual waste production in Ukraine reaches nearly 500 million tons [1].Nevertheless, there are still no defined practical solutions for the effective waste disposal.

Reports on research projects
(2016), «EUREKA: Physics and Engineering» Number 4 Given great variety of mining industrial waste types, special attention should be paid to auriferous ore flotation tailings, main part of which is never used and accumulated in dumps, storages and sumps.Considering that the gold percentage is distributed very unevenly and ranges from 10 to 100 gr/ton, it influences the accumulation of the auriferous ore dump flotation tailings [2][3][4][5].Until present, the main treatment method for this waste type is ground storing which causes adverse ecological situations that manifest themselves in deterioration of sanitary and hygienic conditions, violation and change of natural landscapes and loss of natural resources.
It should be also mentioned that this waste type has heavy metals in its composition: lead, manganese, zinc, Fe, which by decision of the UNECE are attributed to the most hazardous group [6,7] and, respectively, one of the priority targets for control and regulation.Affected by the atmospheric precipitations and weathering, leaching of heavy metals takes place from the auriferous ore flotation tailings, which results in polluting materials emission into the air, water and soil [8,9].This is why it is a priority task to look for technical and technological solutions in the area of the abovementioned waste utilization into environment friendly products, including construction materials.
Certain proposals are known of waste disposal that include heavy metals in construction materials production using classical cement systems [10][11][12][13] which have low efficiency due to the low fixation stability in the artificial stone compound and as a result have limited application ability.The future-proof solution for the auriferous ore flotation waste disposal in the composition of construction materials and heavy metals localization is the use of slag-alkaline cement as a viscid materials developed by Scientific-Research Institute for Binders and Materials (SRIB&M).In this way, known solutions [14][15][16][17] show quite high localization reliability of radioactive, including heavy, metals in the composition of slag-alkaline cements that allow fixing the elements reliably inside the material structure at both physical and chemical level.Known data of foreign researchers [18,19] also show high efficiency and reliability of heavy metals localization in the compound of slag-alkaline viscid systems.This is why the current study is conducted on recycling of auriferous ore flotation tailings by binding it as a cement component, which also can be one of the effective applications for this type of waste.

Raw Materials and Research Methods
As a test systems during research of structuring processes in the "slag-alkaline cementheavy metals" system, a slag-alkaline viscid material was used based on the blast furnace granulated slag from Ilyich Iron and Steel Works of Mariupol with М о =1.1 and the alkaline component in the form of sodium metasilicate pentahydrate that was inserted into cement compound in a dispersed form.During production of slag-alkaline cement, sodium lignosulfonate was also additionally inserted for providing acceptable solidification times.Fe 3 О 4 , MnO 2 , Pb 2 O 3 were used at 10 wt.% percentage in viscid composition as a heavy metals compounds.
Auriferous ore flotation enrichment dump tailings (DT) from the Sauliak field were used as a real waste containing heavy metals.
Chemical composition of the raw materials is shown in Table 1.

Chemical Engineering
After inserting of heavy metal compound MnО 2 in the slag-alkaline cement (Fig. 1, cur.3), phased composition of the artificial stone hydration products after 28 days of solidification is characterized by additional presence of rhodonide -MnO•SiO 2 (d=0,308; 0,293; 0,275; 0,252) and pumpellyite (d=0,286; 0,208; 0,160), that also shows the ability of the mentioned heavy metal to participate in the process of structuring of alkaline viscid compositions.Presence of rhodonide is confirmed by DTA through the indexes of internal effects at the temperature of 780 °С.
The reliability of the chemical bonds of heavy metal elements in structuring compounds of the artificial stone based on alkaline viscid systems was studied through "slag-alkaline cement + dump tailings"."PC I-500 + dump tailings" was also studied (Table 2) as a system for comparison.Chemical stability of the compounds was defined by leaching the metals in a contact environment.Distilled water, saline (pH-11) and acid (pH-3) solution was used as a contact environment.Before testing the samples, cylinders (h=60, d=30 mm) after 28 days of solidification, were put in contact with the environments at the rate 1 to 10 accordingly sample volume to a contact environment volume.After that, the samples were exposed during 7, 14, 28 days.For quantitative evaluation of the leaching grade of the metal, the method of atomic spectroscopy was applied.
Processing and analysis of the sample, containing dump tailings, leaching results (contact environment distilled water) showed the high grade of chemical binding the Mn, Fe elements in the "slag-alkaline cement + dump tailings" (№ 1) where percentage of dump tailings was 20 % (Table 2).After increasing the percentage of dump tailings up to (30 %) in the cement it showed a partial leaching of Fe (0,05 mg/l).On the other hand, when dump tailings were used as a part of PC I-500 (№ 3), it showed leaching both Mn (0,01 mg/l) and Fe (0,3 mg/l), that proves the low level of chemical binding of these elements.
After changing the contact environment (saline or acid solution), it showed quite intense leaching of heavy metals in both Portland (№ 3) and slag-alkaline (№ 1, 2) cement systems.However, the heaviest was leaching noticed in the "PC I-500 + dump tailings" system.In this way, during the use of dump tailings in compound of PC I-500 (№ 3), it showed leaching on 28-th day (saline contact environment), of both Mn (0.28 mg/l) and Fe (3.9 mg/l), which is accordingly 100 % and 78 % more than "slag-alkaline cement + dump tailings (20 %)" system -Mn (0.14 mg/l), Fe (2.2 mg/l).
With replacement of the contact environment from saline to acid solution, leaching of heavy metals increases.However, leaching on 28-th day of both Mn (36.7 mg/l) and Fe (253 mg/l) in "PC I-500 + dump tailings" system is 130 % greater and relatively 60 % greater than "slag-alkaline cement + dump tailings" system as well.In this way, data on participation of the studied heavy metals in structuring of artificial stone bindings was obtained, also it showed the reliability of binding the target elements in slag-alkaline

Fig. 2 .Fig. 3 .
Fig. 2. Change of initial setting time and compressive strength of slag-alkaline cement (alkaline component -Na 2 SiO 3 •5H 2 O) that has a dump tailings admixture At the same time insertion of dump tailings into PC I-500 composition (Fig. 3) results in the extension of the solidification times and reduction of the cement stone durability.

Table 1
Chemical Composition of the Raw Materials 3M and differentially thermal analysis (DTA) by derivatograph of R. Paulik, J. Paulik, and L. Erdey system, MOM (Budapest).The heavy metals bonds stability in the compound of cement matrix was studied through method of leaching elements by atomic spectroscopy.Compressive strength of cement (40×40×160 mm) was determined according to DSTU B V.2.7-187:2009.The conditions of samples solidification were normal: temperature t=20±2 о С, moisture W=95±5 %.
-The processes of structuring viscid compositions in the presence of heavy metals were studied with the help of physical and chemical methods of analysis: X-ray analysis by diffractometer

Table 2
Intensity of Leaching of Heavy Metals from Viscid Compounds Containing Dump Tailings