Utilization of calcite-rich Green Liquor Dregs (GLD) by-products from pulp and paper industry: Cement clinker production and life cycle analysis

Abstract

The pulp and paper industry produces several calcite-rich by-products including Green Liquor Dregs (GLDs), lime mud, grits, sludges, etc. Presently, majority of these by-products are managed by landfilling. The GLD used in this study is mainly dominated by calcite (∼80 %) and Hydrotalcite like compounds (HTlc, ∼12 %). It is used to produced OPC clinkers by using them as 0 %, 5 %, 10 %, 15 %, and 20 % replacement of limestone used for clinker production. TGA-DSC analysis of the clinker raw meals up to 1350 ℃ indicates that increase in GLD leads to slight reduction in the decomposition temperature for the raw meals, and a slight change in the formation temperatures for C2S and C3S. The mineral phase compositions of all the clinkers are comparable with a slightly decreasing C3S and C2S with increasing GLD. Compared to the Bogue calculated compositions, C3S and C2S are slightly lower, while the C3A is significantly lower and C4AF is significantly higher. The environmental leaching of GLD and the clinkers are all within the limits set by EN-12457-2. The environmental impact of clinker production and effect of GLD is analyzed for cradle-to-gate scenario with system boundaries. This analysis shows that by using GLD as replacement for limestone can lower the impact on diversity as well as CO2 related to transportation can also be reduced.