| Mine tailings,as one of the largest solid waste streams in China,still have a low utilization rate under the current economic and technological conditions.Exploring new solutions for the utilization of mine tailings has become an inevitable request for the ecological civilization construction and sustainable social development of China.In this paper,the pozzolanic activity and hydration properties of the siliceous gold mine tailings after mechanical activation were studied for the purpose of the utilization of mine tailings as resources,and the results provided a theoretical basis for the evaluation of pozzolanic activity and hydration propertis of the siliceous tailings.Based on the characteristics of activated tailings,the mine tailings-based composite Portland cement were prepared,which provides a new approach for the utilization of mine tailings.The research of the pozzolanic activity of the siliceous gold mine tailings indicated that the pozzolanic activity can be improved by mechanical activation,and it was affected by the particle size,specific surface area,crystallization degree,and chemical and phase compositions of mine tailings.After mechanical activation,the activity index of the siliceous gold mine tailings was 75.63%.Different mineral phases in mine tailings have different contributions to the improvement of pozzolanic activity of activated mine tailings.The mineral phase mica in mine tailings has the highest degree of amorphization,followed by the mineral phase feldspar,and the mineral phase quartz exhibited the lowest amorphous degree.The degree of amorphization of the above three types of minerals was 63%,45.1%,and 19.1%,respectively.The research of the pozzolanic activity of the typical minerals in gold mine tailings revealed that the particle size,specific surface area and pore content of different minerals exhibited different change rules during the activation process.However,the degree of amorphization,alkali leaching rate,and pozzolanic activity index of the minerals exhibited an increasing trend with the increasing of grinding time and specific surface area.When the specific surface area of the mica powder was 28.82m2/g,the values of alkali leaching rate,pozzolanic activity index,and degree of amorphization were observed at 40.38%,94.36%,and 85.01%,respectively.More so,6.08m2/g specific surface area of feldspar powder had alkali leaching rate,pozzolanic activity index,and degree of amorphization values of 14.58%,83.01%,and 57.63%,respectively.Meanwhile,quartz powder had alkali leaching rate,pozzolanic activity,and degree of amorphization values recorded at 9.09%,76.4%,and 44.64%,respectively,when the surface area was 5.63m2/g.The presence of silicoaluminate minerals mica and feldspar in mine tailings is helpful to improve the pozzolanic activity of mechanically activated mine tailings.The study on the hydration properties of siliceous gold mine tailings indicated that the activated tailings possessed the basic characteristics of pozzolanic materials,it can can react with Ca(OH)2 to produce cementing products in the presence of water at room temperature,showing hydraulicity.The concrete manifestation is:the activated siliceous mine tailings can react with Ca(OH)2 to form amorphous C-(A)-S-H gel in the presence of water at room temperature,and ract with CaO and CaSO4 to form amorphous C-(A)-S-H gel and fiber-like ettringite.The compressive strength of alkali-activated tailings pastes increased with the increasing of curing time.The results of the studies on the hydration properties of mine tailings at mineralogy angle showed that amorphous C-S-H was the main hydration product of CaO-activated quartz paste,and amorphous C-(A)-S-H gel was the main hydration product of CaO-activated feldspar and mica pastes.A small amount of tratlingite and hydrotalcite-like compounds can be detected in the CaO-activated mica paste.The change of CaO content affected the development of the compressive strength and the content of hydration products,but has no obvious effect on the types and morphology of hydration products.The main hydration products were C-(A)-S-H gel and fiber-like ettringite in the CaO-CaSO4 activated feldspar and mica pastes.The fiber-like ettringite filled in the pores and cracks of the pastes and interwove with the amorphous C-(A)-S-H gel to cover the surface of the unreacted particles to form a network structure,which was conducive to the development of macroscopic strength.The application of the activated siliceous gold mine tailings showed that the tailings can be used as cement active admixtures.The addition of the mechanically activated tailigns caused the secondary hydration reaction of the tailing-based Portland cement.During the hydration process,the activated tailings can react with Ca(OH)2,the major hydration product of cement,to form C-(A)-S-H gel.At 10%addition of the taillings powders,the basic performance of the tailing-based Portland cement,such as compression/flexure strength,setting time,and stability,can meet the requirements of 42.5 cement,and at 30%addition,can meet the requirements of 32.5 cement.The studies on the hydration kinetics of the tailings-based composite Portland cement showed that the addition of tailings reduced the rate of hydration heat evolution and hydration heat.The hydration process of the composite cement was controlled by NG,I,and D processes,and its hydration process conforms to Krstulovic Dabic model. |
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