Statistical analysis and optimization studies on recovery of carbon from steel plant sludge

Abstract

Steel-making industries that produce sludge as a by-product in their operations contain valuable mineral phases and carbon which can be recovered for primary and secondary usage. The present study aims to recover carbon values from the sludge, adopting flotation technique by altering the surface hydrophobicity of carbon values and optimizing its process parameters for effective separation. Laboratory scale studies were carried out in a D12 Denver flotation cell using a laboratory-synthesized flotation reagent as the collector for carbon recovery and Methyl Isobutyl Carbinol (MIBC) as the frother. The experimental study was statistically designed using the Taguchi method with three input variables, i.e., frother dosage, cell revolutions per minute (rpm), and collector dosage at mixed levels for process parameter optimization and for interpretation of the importance of process parameters on the mean and variation of responses. Experimental designing and statistical analysis were used to study the effects of input parameters on outputs and determine the order of significance. Among L18 (2^1*3^2) orthogonal array experiments performed, the one with operating conditions at 1400 rotations per minute (rpm) of the cell, frother dosage of 54 g per tonne (gpt), and collector dosage of 3400 g per tonne (gpt) of feed, 83.05% carbon recovery was optimally obtained. Based on the flotation experimental test results, one-way analysis of variance (ANOVA) was used to predict the order of significance of three input variables for each response variable namely, carbon grade and carbon recovery. The order of significance for the response parameter, carbon recovery, was observed to be in the order of Collector dosage > Frother dosage > Cell rpm indicating the impact of the laboratory-synthesized collector on recovering the carbon values from the sludge.