@conference{
author = "Đokić, Jovana and Štulović, Marija and Korać, Marija and Anđić, Zoran and Kamberović, Željko",
year = "2023",
abstract = "More than 90% of lead produced in Europe comes from secondary lead flows, of which 85% is attributed to waste lead-acid batteries (LAB). The main technological approach for LAB processing implies pyrometallurgy by which 100–400 kg of waste slag (WS) is generated per 1 ton of produced metallic lead. Due to recycling process parameters, generated WS has great potential for releasing toxic elements contributing to environmental pollution [1]. Namely, the most common flux in the recycling process is sodium-based (Na2CO3) when alkali lead waste slag (ALWS) is generated, characterized as hazardous due to its physical-chemical characteristics: high leachability, hygroscopic and pulverized nature and, ultimately, instability [2,3]. Therefore, ALWS treatment prior to disposal should be considered an integral part of waste LAB treatment systems. Immobilization of toxic elements contained in slag is crucial and can be achieved by stabilization/solidification processes (S/S) as one of the most widely used technologies in the treatment of heavy metal-containing wastes for final disposal or utilization.
In this research, ALWS generated in the waste LAB recycling is used to determine the S/S process efficiency as a function of the added binder amount (cement, in the range of 5 – 10 %), pre-treatment (the removal of water-soluble compounds), and activator addition (MgO). The liquid to solid (L/S) ratio was 1/4 in all S/S experiments. The basic parameters for the effectiveness assessments were compressive strength (UCS) and pollutants leaching (Method 1311 Toxicity characteristic leaching procedure, TCLP).
ALWS containing 3.5 Pb, 15.5 Na, 14.0 S, and 24.7 Fe was mixed with cement and water. The results of UCS showed that all produced solidificates exceeded the required value of 0.35 MPa [4], yet the mixture containing 7.5 % of the cement has the best mechanical properties (2.1 MPa). This sample was further analyzed and the TCLP results showed that the Pb concentration exceeds the limit values for stabilized slag (10.4 and 5 ppm, respectively). In the next set, ALWS was pre-treated by continuous rinser (30 ºC, 60 min, L/S 4). Obtained results of UCS (0.4 MPa) and TCLP (53.4 ppm) were unfavorable. The last set, besides the binder, included activator addition (MgO, 7.5 %) altogether with a high content of untreated ALWS (85 %). Analysis of the produced solidificates showed favorable and acceptable results (USC - 3.3 MPa, TCLP – Pb 4.5 ppm).
Generally, in an alkaline slag-leaching solution lead precipitates as a complex mixture (PbO, Pb(OH)2, PbO×Pb(OH)2). Lead oxides are amphoteric and dissolve in an alkaline aqueous solution, leading to poor solidification. Also, lead present in surface coatings around cement grains prevents cement hydration. Simultaneously, the migration of lead to the surrounding water is promoted. The negative effect of the pre-treatment is a consequence of the sulfate ions absence, as well as the absence of the ettringite (Ca6Al2(SO4)3(OH)12×26H2O) and sulfate- AFm phases [5], which negatively affect the strength of the product. The addition of MgO benefits the S/S process through hydrotalcite-like phase formation ([M1-
2+M 3+(OH) ][A n-×mH O], M2+=Mg, Zn, Ni, Fe; M3+=Al, Cr, Fe; A=CO 2-,
NO -, Cl-), a compound capable of metal adsorption, hence immobilization [6].
The conclusion is that, contrary to the pre-treatment process, the addition of MgO has an overall positive effect on the S/S process of ALSW, ensuring both mechanical and chemical stability. This ALWS solidificate, obtained through the S/S process by using MgO as an activator, is safe for disposal, according to environmental regulations.",
publisher = "Belgrade : Serbian Chemical Society",
journal = "9th Symposium Chemistry and Environmental Protection EnviroChem2023 with International Participation, Book of Abstracts, Kladovo, June 4-7, 2023",
title = "Stabilization/solidification process of alkali lead waste slag: influence of pretreatment and addition of selected additives",
url = "https://hdl.handle.net/21.15107/rcub_cherry_6236"
}
