Geotechnical and Geo-environmental Assessment of Process Waste from Steel Industries and its Stabilisation

Abstract

Process waste is a by-product from steel industries. In India, large quantity of process waste is produced from steel industries as most of engineering demand is fulfilled by these plants. During the combustion of iron ore, produced flue gases are collected and allowed to pass through a plant known as Gas exchanger Plant (GEP) in which water is injected in the form of spray. After separation from the flue gases, particles are taken into another unit known as Rotatory settling tank (RST) in which particles are allowed to settle down and these settled particles are termed as process waste. It’s been converted into slurry form and transported to disposal site through pipeline system. Daily production of process waste from plant is approximately 600m3 per day.

As production is on large scale, land acquisition will be more for the disposal of the waste product. In plants like NSPCL, Bhilai due to scarcity of land, as a result starter dyke of the storage lagoon has reached to its full capacity. To increase the capacity of the lagoon, the dyke is to be raised by standard upstream raising method. But due to poor strength of the material inside the lagoon, machinery movement is not feasible as large settlement was observed. To overcome such industrial problem, an investigation on geotechnical and geo-environmental assessment of the process waste is carried out and reported here. The possible methodology either to utilize this material or stabilization of this material inside the lagoon is investigated to overcome such industrial problem.

In the first phase of the project, Geotechnical characterization was carried out comprising of specific gravity, particle distribution, determination of shear, compaction, consolidation and hydraulic conductivity parameters and California bearing ratio followed by XRD, SEM for determination of mineral and shape of particle and CEC.

In the second phase of the project, Geo-environmental characterization was carried out comprising of determination of pH, soluble sulfate, zeta potential and lime reactivity to check the feasibility of material to be used in the cement industries. Further Batch leaching test was done to find the toxicity characteristics of the process waste.

After characterization it was found that material strength in the saturated state was very low (California bearing ratio soaked condition experiment) and hence lime was mixed with the material in order to improve the strength in saturated condition so as to use the material in pavement construction.

Process waste was mixed with 2%, 4%, 6%, and 8% of lime and, standard proctor test was performed, to obtain corresponding MDD and OMC. Various calfornia bearing ratio samples were prepared for un-soaked and soaked conditions. Un-soaked samples were tested immediately after the sample preparation and soaked samples were tested after curing period of 96 hours. Variation in the CBR value was observed for both un-soaked and soaked condition with the varying content of lime.