Arabian Journal for Science and Engineering https://doi.org/10.1007/s13369-020-05065-6 RESEARCH ARTICLE-CHEMICAL ENGINEERING Utilization of alkaline Aluminosilicate activation in heavy metals immobilization and producing dense hybrid composites H. M. Khater 1 · Mahmoud Ghareib 1 Received: 29 April 2020 / Accepted: 23 October 2020 © King Fahd University of Petroleum & Minerals 2020 Abstract Recently geopolymer technology possesses not only great efficiency in immobilizing heavy metal wastes but also produces valuable materials that can be applied in building sectors. The aim of this study is to examine the capability of geopolymers in the immobilization and entrapping of heavy metals bearing materials. The study will focus on the evaluation of optimum ratio of heavy metal that can affect and densify the produced composite. The studied mortar’s binder was made from blast furnace slag, while the used fine aggregates were air-cooled slag<1 mm. However, the used activator was 8% sodium hydroxide. The studied heavy metals’ bearing materials were barium sulfate, lead phosphate, lead slag and electric arc furnace dust used as partial replacement of blast furnace slag. The physico-mechanical characterization of each set of samples was conducted using XRD, FTIR, SEM, compressive strength and bulk density. Results demonstrated that barium sulfate can be efficiently used up to 2%, lead phosphate up to 1%, lead slag up to 5% and electric arc furnace dust up to 10%. Keywords Heavy metals · Immobilization · Activation · Density · Mortar 1 Introduction Heavy metal immobilization is taking great attention from scientists worldwide especially with an increasing concern regarding sustainability awareness. Many industrial and res- idential wastes as those from mining and metallurgical industries contain many significant amounts of heavy metals. However, preventing their release into the ecosystem takes the attention of most of ecological experts. Heavy metals contaminants that are supposed to be efficiently immobilized by ferrosilicate glasses possess slight leachable characteris- tics, while slag wastes are treated simply by dumping either in landfills or in the sea [1]. There are many techniques to process heavy metals containing materials safely worldwide, among them are the ones based on solidification/stabilization using cement-based technologies [2, 3], together with alkali- activated slags as well as other alternative binding systems [3–5]. The most promising technique for waste treatment applications and immobilization of toxic contaminates is alkali activation of aluminosilicate binders [6–10] as favored B H. M. Khater hkhater4@yahoo.com 1 Housing and Building National Research Centre (HBNRC), 87 El-Tahrir St., Dokki, Giza, Cairo P.O. Box 1770,, Egypt by their low permeability, high acid resistance and durability as compared with traditional Portland cements [6, 8, 10, 15]. Also, the use of alkaline activation technology in stabilization of various toxic and radioactive wastes has been investigated over a number of years [10–16], while the process by which the contaminants incorporate into the geopolymer network is not clearly understood. There are several possible geopolymer applications in toxic metals immobilization, from which few concerning the relationship between heavy metals and geopolymer paste after structural integrity. Also, many heavy elements incor- porated in the waste materials are tightly locked in 3D geopolymer network in either strong physical or chemical way [6–9]. The immobilization process depends mainly on the type of immobilized element [7], whereas studies prove that geopolymers can be considered as the useful tool for immobilization of many heavy metals [8]. The metals’ immobilization efficiency in any binding materials is intensely correlated to the microstructure of the binder, as well as the pore size distribution, pore shape and total porosity. Deja [9] studied the chromium, cadmium, zinc and lead ions immobilization in alkali-activated slag binders, where the results depict the essential role of microstructure as well as phase composition of hydrated slag in their immobi- lization. Also, the type of the immobilized ion affects the 123