The Use of High-Alloyed EAF Slag for the Neutralization of On-Site Produced Acidic Wastewater: The First Step Towards a Zero-Waste Stainless-Steel Production Process

Abstract

Recycling of steelmaking slags has well-established applications, such as their use in cement, asphalt, or fertilizer industries. Although in some cases, such as the electric arc furnace (EAF) high-alloyed stainless-steel production, the slag’s high metal content prevents its use in such applications. This forces companies to accumulate it as waste. Using concepts such dematerialization, waste management, industrial symbiosis, and circular economy, the article drafts a conceptual framework on the best route to solving the landfilling issue, aiming at a zero-waste process re-design. An experimental part follows, with an investigation of the use of landfill slag as a substitute of limestone for the neutralization of acidic wastewater, produced by the rinsing of steel after the pickling process. Neutralization of acidic wastewater with both lime and slag samples was performed with two different methods. Two out of four slag samples tested proved their possible use, reaching desired pH values compared to lime neutralizations. Moreover, the clean waters resulting from the neutralizations with the use of both lime and slag were tested. In terms of hazardous element concentrations, neutralization with slag yielded similar results to lime. The results of these trials show that slag is a potential substitute of lime for the neutralization of acidic wastewater.

Neutralization of Acidic Wastewater from a Steel Plant by Using CaO-Containing Waste Materials from Pulp and Paper Industries

“…The initial pH value of the investigated acidic wastewater was in the interval of 1.3 to 2.4. Though the pH of regular water has a value of 7, in this study, the aim was to raise the pH value to 9 since the absorption of some elements (such as Ni) from the reactants are maximized at high pH levels [ 8 ]. Furthermore, flocculants added in industrial applications will significantly lower the pH of the neutralized water.…”

“…In several publications ([ 4 , 8 , 9 , 10 , 11 ]) during the last decade it was reported that steelmaking slags, waste limestone materials from the marble industry [ 12 ], and cement kiln dust [ 13 ] and other secondary lime sources can be successfully applied for neutralization of acidic wastewaters and purification of industrial waters. Lime mud and recovery boiler ash can be used to remove heavy metal contaminations from metal finishing wastewater.…”

A Review of Circular Economy Prospects for Stainless Steelmaking Slags

“…In general, several steel slags have beneficial properties such as good strength, durability, and latent pozzolanic (cementitious) properties that make them attractive and potentially suitable for engineering applications, such as infrastructure construction, soil stabilization, neutralizer, as filler or binder in concrete or as drainage or low-permeability barrier layers [61][62][63][64][65][66][67]. Slags from stainless steelmaking are potential as well provided that the best suitable slag type is selected and modified by appropriate additions, cooling method, or other pre-treatments, i.e., tailoring for each specific application.…”

A Study of Treatment of Industrial Acidic Wastewaters with Stainless Steel Slags Using Pilot Trials

“…The authors of this study have previously proposed a new application of stainless steel slags, which can contribute to the overall reduction in the landfilled output. Several stainless steel slags have been successfully tested as lime replacements for the treatment of industrial acidic wastewaters, generated in situ during the pickling process [9]. Lime is frequently used for the treatment of acidic wastewaters, but the reaction products are also often landfilled.…”

“…Therefore, the aim of this study is to strengthen the technology validation, by replicating the same experiments that are conducted in laboratory settings in upscaled pilot trials. The primary focus of this study is to test whether the pH buffering of industrial acidic wastewaters, using stainless steel slag, can be replicated for bigger volumes than the one used in precedent laboratory trials [9,10]. Moreover, it is of interest to this study to determine the relationship between the volume of wastewaters to treat and the amount of slag needed to do so, when the kinetic conditions are controlled.…”