Research On Alkali-slag-lithium Slag Cement

Environmental protection has became a global focus, and green technology accepted by people. In building material production, green technology obviously means green building material. The production of green building material applies clean manufacturing technology, consumes low power, and uses large quantity of industrial or urban solid waste and little natural resources. But the production of cement, which owns huge production and consumption in building material, costs large energy, makes high pollutions, which doesn't meet the requirement of green building material. Industrial residue containing silicon oxide and aluminum oxide have potential activity. Making use of them as primary material of cemented material not only releases the load on ecological condition, but also can replace part of cement, which displays waste-utilized and low power waste function. Shehong lithium slag is a muck discharged during the extraction of lithium carbonate based on sulfuric acid technology. Micro analysis shows that the proportion of silicon oxide and aluminum oxide reaches 84.2%, and amorphous glass phase is generally observed. But it can not hydrate and harden under natural conditions as its alkalinity is 0.044 and quality index 0.39, which leads to the difficulty of being activated. So its uses are limited in admixture for cement or mineral admixture for concrete, which can not make full use of its potential activity. This paper made research on activated methods of low alkalinity and quality index's lithium slag. Adding another industrial residue-slag, undergoing drying and screening processes, and choosing proper alkali activators, the alkali-activated cemented material which contains no clinker and can normally hydrate and harden in natural conditions is made up. The proportion of lithium slag in the cemented material varies from 20%~50%. As to the strength of cement, 7d bending strength reaches 6.72MPa~8.60MPa, 7d compressive strength reaches 24.3MPa~35.4MPa; 28d bending strength 7.89MPa~ 10.58MPa, 28d compressive strength 31.3MPa~57.4MPa; 56d bending strength 10.45Mpa~11.70MPa, 56d compressive strength 53.8MPa~68.8MPa. Effects of cemented material ratio, types of alkali activator and quantity of alkali on bending strength, compressive strength and setting time are studied, as well as the durability such as resistance to sulfate attack and acid corrosion. The results indicate that proper alkali activators are the critical material for strength growth. The composite activators of J1 and J4 or J2 and J4 both are the good choices. The quantity of alkali varies in certain range. As to composite activators of J1 and J4, due to the special craft, its proportion is approximately fixed in 5% so as to making the initial time not earlier than 40min; as to composite activators of J2 and J4, the strength achieves peak when their proportion reaches 6%. The setting time of lithium mortar is mainly affected by the proportion of lithium slag when the proportion of lithium slags below 40%. And under the same condition, the proportion of lithium slag doesn't affect the later mortar strength. The bending and compressive strength of slag-lithium slag mortar in 56d are as the same of slag mortar. Sulfate attacking tests show that slag-lithium slag mortar has good resistance to sulfate attacking, whose corrosion index is below 0.95. Acid corrosion tests show that strength percentage loss is below 2%. Under the same conditions, the corresponding values of slag mortar are 0.96 and 1.45%. Obviously slag-lithium slag cement's abilities of resistance to sulfate and acid haven't decreased. The hydrate of slag-lithium slag mortar is analyzed by the means of XRD and SEM. Insoluble zeolites are observed except for C-H-S. Hydrate mechanism of slag-lithium slag mortar is initiatively discussed. The results indicate that during the hydration of alkali-activiated slag-lithium slag cement, alkali reacts with slag, generating C-H-S and etc. and lithium slag reacts with hydrate of slag, forming insoluble zeolites, which are inserted in the hardenite of slag serving as micro framework. So the later mortar strength of modified lithium slag nearly reaches the corresponding values of slag mortar. This type of alkali-activated cemented material is composed with industrial residue, containing no clinker. Strength grade is equivalent with 32.5~52.5 Portland cement when the proportion of lithium slag varies in the range of 20%~40%. The capabilities of sulfate and acid resistance are excellent, thus it is a green cemented material especially suitable in uses under acid medium conditions.