Steel slag quality control for road construction aggregates and its environmental impact: case study of Vietnamese steel industry—leaching of heavy metals from steel-making slag

Abstract

Steel slag is an industrial by product of steel manufacturing processes and has been widely used in countries like Japan, United States, and European Union nations. However, the current utilization of steel slag in Vietnam is very low mainly because of lack of quality control of slag treatment and chances for reuse of treated steel slag. This paper presents the current steel slag production status and its potential to use as road construction aggregates in consideration of environmental and quality control issues. The basic oxygen furnace (BOF) and electric arc furnace (EAF) slag samples were collected from the seven large steel making factories of Vietnam and brought back to evaluate leaching amount from the slags. The batch leaching test methods were performed at laboratory using the leaching test of steel slag roadbed material in Japan (JIS K 0058 − 1) and Toxicity Characteristic Leaching Procedure (EPA method 1311) widely adopted in Vietnam. The results show that pH level and parameters such as T-Cr, Ni, Cu, Pb, As, Mn differ from the two test methods. The EPA 1311 seems too harsh to evaluate the environmental impacts because in the operation condition of the road, acidic liquid is absent. It is concluded that JIS test, which uses fresh water with gentle mixing not to degradation in size while leaching, is suitable for the evaluation, for the environmental assessment in service of the slag aggregate for roadbed.

Exploring the Potential for Steel Slags Valorisation in an Industrial Symbiosis Perspective at Meso-scale Level

“…Finally, a considerable difference can be noted with regard to the part of slag classified as “waste” and destined for disposal: while the percentages of EAF slag classified in this way have ranged from 27 to 52% of the total, depending on the year, those of LFS slag have always reached 99% of the total, denoting a reduced, if not null, demand for the material on the market and further highlighting the difficulties of the management, treatment and reuse of this type of slag. Even though EAF are recovered in higher percentage respect to LFS (ranging from 50-to 80% of the total production) and the recovery options are wide (aggregate for road construction [ 16 , 22 – 25 ], partial replacement of cement [ 6 , 7 , 26 , 27 ], natural aggregate in concrete [ 28 – 42 ]), the classification as by-product it still appear low highlighting critical issues still present in Italy that hinder producers in managing these residues as by-products. As consequence producers prefer divert their residues to dedicated treatment plants.…”

“…In addition to the primary material (molten steel), the so-called “ Basic Oxygen Furnace slag ” (or “ BOF ”) derived from the combination of the impurities with lime and dolomite, is also tapped from the converter, in a range of approximately 100–150 kg per tonne of steel produced. This type of slag is mainly used as aggregate in road construction [ 3 , 14 – 16 ], as well as other minor reuses in concrete production [ 17 – 19 ] or as an addition in fertilisers [ 20 , 21 ]. Figure 1 shows, in summary, the two steps of the integral cycle.…”

“…Within the furnace, different reactions take place, which result in the formation of the primary material (molten steel) and the so-called “ Electric Arc Furnace slag ” (or “ EAF ”), in a range of approximately 150–180 kg per tonne of steel produced. This type of slag is divided into two categories, depending on whether the steel produced is carbon steel (“ Electric Arc Furnace slag from Carbon steel ” or “ EAF-C ”) or stainless/high alloy steel (“ Electric Arc Furnace slag from Stainless/high alloy steel ” or “ EAF-S ”) and is mainly used as aggregate for road construction [ 16 , 22 – 25 ] or as a partial replacement of cement [ 6 , 7 , 26 , 27 ] and/or natural aggregate in concrete [ 28 – 42 ]. The steel produced in both processes is then usually destined for secondary metallurgy operations in ladle furnace (e.g.…”

Overview of cement and concrete production in Latin America and the Caribbean with a focus on the goals of reaching carbon neutrality

“…There is a huge question of contamination by heavy metals, but the amounts are really small at the end of the day. Leaching studies have demonstrated that when used in road construction, the concentration of heavy metals in the leachate is far below standards for industrial wastes [43]. The application in cementitious systems, which have a significant encapsulation capacity of heavy metals, seems an even safer alternative.…”