Investigations on phosphorus recovery and reuse as soil amendment from electric arc furnace slag filters

Abstract

Electric arc furnace (EAF) steel slag has been identified as an effective filter material for the removal of phosphorus (P) from both point and non-point sources. To determine the feasibility of land-applying P saturated EAF steel slag this study was undertaken to investigate (i) saturated EAF steel slag material's potential as a P fertilizer or soil amendment and (ii) P desorption and metals leachate from saturated EAF steel slag material to surface runoff. Medicago sativa (alfalfa) was planted in a nutrient depleted washed sand media. Phosphorus was added either as saturated EAF steel slag or as a standard commercial phosphate fertilizer in order to assess the plant availability of the P from saturated EAF steel slag. Four different P application levels were tested: a low (20 lbs acre furrow slice⁻¹ (5.5 g P m⁻³)) two medium (40 and 60 lbs. acre f.s.⁻¹ (11 and 16.5 g P m⁻³)) and a high (120 lbs. acre f.s.⁻¹ (33 g P m⁻³)). The above-ground biomass of half of the plants was harvested after 5 weeks and the second half at 10 weeks. All treatments regardless of the P source used showed high rates of germination. At the first harvest period (5 weeks) significantly higher above-ground biomass (p < 0.01) was seen at the 3 highest P amendment rates in treatments with triple super phosphate fertilizer (TSP) than with EAF steel slag. However, by the second harvest (10 weeks) only the highest amendment rate of TSP showed a significantly higher amount of biomass (p < 0.01), suggesting that EAF steel slag might be an effective slow release P source. In a second experiment, a rain simulator was used to assess desorption of DRP, TP and metals from a saturated and semi-saturated EAF steel slag. The results revealed that the total amounts of DRP and TP released to surface runoff from EAF steel slag were negligible when compared to the total quantities of P retained by this material. Overall the results from this study demonstrated that once the EAF steel slag filter reaches its saturation point, the material could be re-used as soil amendment for the slow release of bioavailable P with minimal risk for loss of P to surface runoff, bringing further benefits to the environment.

Keywords:

• Phosphorus
• steel slag filters
• dairy effluent
• Medicago sativa
• rain simulation

Acknowledgments

The researchers would like to thank Senator Patrick Leahy for providing financial support to the USDA Natural Resources Conservation Service (NRCS) Alternative Manure Management program, which funded this research. We would also like to thank Mr. Michel Piche, MultiServe, Quebec, Canada for supplying the EAF steel slag used in these experiments. Mr. Eamon Twohig for his assistance in laboratory analysis.

Notes

*Reference soil (Soil); Electric Arc Furnace Slag A (EAFA); Electric Arc Furnace Slag B (EAFB); mixture of 50% Electric Arc Furnace Slag A and 50% soil (EAFA/Soil); mixture of 50% Electric Arc Furnace Slag B and 50% soil (EAFB/Soil).

**Values in parentheses are the DRP lost to surface runoff expressed as a mass percentage.

*Reference soil (Soil); Electric Arc Furnace Slag A (EAFA); Electric Arc Furnace Slag B (EAFB); mixture of 50% Electric Arc Furnace Slag A and 50% soil (EAFA/Soil); mixture of 50% Electric Arc Furnace Slag B and 50% soil (EAFB/Soil).