The Preparation Technology And Mechanism Research Of The Lightweight Aggregate Made From High Carbon Ferrochrome Slags

High carbon ferrochrome slag is a waste of by-products in the manufacturing process of ferrochrome at 1700°C. With a property of high viscosity and melting point, it is difficult to separate the residual iron from the slag. So when 1t ferrochrome are produced there wi ll generate about 1~1.2 t residual slags. According to statistics, the discharge of the slag is rising at an annual rate of 40 0,000 tons, and most of them pile as waste residue. It’s not only a waste of land resources, but also a pollution of environment. In the paper, the slag is used to prepare light weight aggregate, it has an advantage of energy and land conservation, waste recovery and environmental protection, and will make a positive significance on the develop of new wall materials and the comprehensive utilization of slags.In the paper, high carbon ferrochrome slag and clay are used as main raw materials to prepare light weight aggregate, and the influence of slag content, firing system and cooling ways on the property of light weight aggregate a re researched. By exploring the expansion mechanism, a suitable mix proportion and firing system with higher utilization of slag and better expansion property are obtained.The results indicated, with an increase of the slag content, the firing temperature becomes higher, the sintering range becomes more narrow and the expansion property becomes worse. The adding of clay can improve the sintering property of aggregate properly. Because at the temperature around 1000 ℃, the clay begins to melt and generates amount of liquid, this can lower the firing temperature effectively. It also shows the aggregate acquires an excellent expansion when the slag content is between 50 percent and 70. The firing process is divided into 2 stages, firstly the green pellets are p reheated before they are fired at high temperature. The influence of firing system is described as follows, with the rising of preheating temperature, the pores formed inside the aggregate become finer and smaller, accordingly with an increase of the appar ent density and particle strength. The expansion of aggregate has a close connection with firing temperature and soaking time, when they increase, the apparent density generally tends to decrease, and the particle strength increases first and then decreases. The cooling types have a strong impact on particle strength. When cooling rapidly, it forms a structure with uncomplete crystal, and the aggregates will become more crisp as the exist of micro-cracks. When cooling slowly, it could form a continuous structure, and crystal grow more completely, which results as the particle strength of slow cooling aggregate is 5.173 times higher than that of rapid cooling.In summary, the best mix proportion and firing system are as follows, the slag content is 60 %, slag content is 27%, foaming agent is 3%, fluxing agent is 5% and water glass is 5%. The green pellets are preheated at 600 ℃ for 20 min, then fired at 1210℃ for 10 min, the final products are cooling in the furnace till to the ambient temperature. The obtained aggregates show an excellent property, the apparent density is 691 Kg/m3, the particle strength is 6.82 MPa, and the water absorption is 3.33%, which can meet the demand in stand ard GB/T 174312-2010 about the aggregate of 700 kg/m3. The surface of aggregate is like the sheeny enamel shell, which can prevent the water permeating in the aggregate. The honeycomb porous structure can make the aggregate has the advantage of light-weight and heat insulation. The results of XRD, SEM and EDS show that, the structure of aggregate is consists of silicate glass, crystal and porosity, and the main crystalline phases include forsterite, spinel, hercynite, enstatite and α-quartz.