Integration of solid residues from the steel and pulp and paper industries for forest soil amendment

Abstract

Beneficial utilisation of process industry residues provides possibilities to reduce energy consumption, to avoid environmental impacts caused by increasing land-filling and promotes sustainable management of natural resources. As traditional utilisation of steel industry residues lies within the realm of civil construction, complementary applications could be found from the integration with pulp and paper industry residues to promote sustainable forest management through forest soil amendment. In our study we show that three different soil amendment matrices, providing slow release and materials handling advantages, were successfully produced according to conventional cement testing practices. The concepts we develop for forest soil amendment incorporate the use of fly ash in tandem with granulated blast furnace or steel slag as binder materials, the utilisation of paper mill sludge as reactive aggregate and the use of green liquor dregs and lime waste from chemical pulping as alkaline components. The neutralising (35.8-38.6%) and reactivity (33.3-38.0%) values (expressed as Ca-equivalents d.w.) with supporting high pH-values (12.9-13.0) indicate liming and buffering capacities of the test matrix materials are comparable to commercial ground limestone products. Additionally, concentrations of Ca, K and Mg and concentrations of Cu, Mn and Zn were found to be higher than organic and mineral soils normally found in the Ostrobothnia region of Northern Finland. Only under severe leaching test conditions (HNO3 and HCl microwave digestion) did the total concentration of Cr in the soil amendment matrix exceed respective Finnish statutory limit value set for the use of fertilisers in forestry. However, as illustrated by the leaching procedure, less than a fifth of the total Cr is likely to become mobile in conditions normally found in nature.</p