Neutralization of red mud with pickling waste liquor using Taguchi’s design of experimental methodology

Abstract

'Red mud' or 'bauxite residue', a waste generated from alumina refinery is highly alkaline in nature with a pH of 10.5-12.5. Red mud poses serious environmental problems such as alkali seepage in ground water and alkaline dust generation. One of the options to make red mud less hazardous and environmentally benign is its neutralization with acid or an acidic waste. Hence, in the present study, neutralization of alkaline red mud was carried out using a highly acidic waste (pickling waste liquor). Pickling waste liquor is a mixture of strong acids used for descaling or cleaning the surfaces in steel making industry. The aim of the study was to look into the feasibility of neutralization process of the two wastes using Taguchi's design of experimental methodology. This would make both the wastes less hazardous and safe for disposal. The effect of slurry solids, volume of pickling liquor, stirring time and temperature on the neutralization process were investigated. The analysis of variance (ANOVA) shows that the volume of the pickling liquor is the most significant parameter followed by quantity of red mud with 69.18% and 18.48% contribution each respectively. Under the optimized parameters, pH value of 7 can be achieved by mixing the two wastes. About 25-30% of the total soda from the red mud is being neutralized and alkalinity is getting reduced by 80-85%. Mineralogy and morphology of the neutralized red mud have also been studied. The data presented will be useful in view of environmental concern of red mud disposal.

The use of red mud as an immobiliser for metal/metalloid-contaminated soil: A review

“…Neutralisation of red mud is recommended to reduce any adverse environmental impact arising from uncontrolled release from storage [110]. Red mud with a pH of 7.0 after treatment with HCl had a decreased capacity to adsorb metals by 30% compared with the untreated red mud with pH 11.5 [47].…”

Optimizing Conditions for Scandium Extraction from Bauxite Residue Using Taguchi Methodology

“…The fundamental advantage of Taguchi method lies in using "orthogonal array" distribution. It allows a much-reduced set of experiments to be done in order to find the optimum settings of involved control factors, at a minimum cost of resources but in a robust way, achieving high rates of reproducibility [62,66,69].…”

“…The Taguchi method is applied through (a) the design phase of the experiment, (b) the calculation of factor effects, (c) the selection of optimum factor levels, and finally at (d) the validation of experimental results stage [66].…”

“…The results obtained indicated four parameters being the most important control factors for Sc recovery and concentration: Acid (H 2 SO 4 ) molarity, Temperature, Solid-to-Liquid ratio (S/L), and Leaching time. In order to study the effect of these parameters on the proposed process, and identify their optimized values, a matrix experiment is set up by appropriately changing their values over a specified range [65,66]. According to the findings of the previous phase and following a symmetric as well as a rational resources' use approach, each parameter is chosen to vary among three values: minimum, middle, and maximum, as shown in Table 1.…”

An Alternative to Clay in Building Materials: Red Mud Sintering Using Fly Ash via Taguchi’s Methodology

“…Taguchi's experimental methodology has been employed to evaluate the pH values. Taguchi's design of experiments has been used extensively in product quality assessment and several other studies [8][9][10][11][12]. Taguchi's fractional factorial design of experiments has been used to examine the effect of significant parameters such as weight of red mud, weight of silicate material added, volume of water, and reaction temperature on the response characteristic (pH of red mud slurry).…”