Mine Clay Washing Residues as a Source for Alkali-Activated Binders

Abstract

The aim of this paper is to promote the use of mine clay washing residues for the preparation of alkali activated materials (AAMs). In particular, the influence of the calcination temperature of the clayey by-product on the geopolymerization process was investigated in terms of chemical stability and durability in water. The halloysitic clay, a mining by-product, has been used after calcination and mixed with an alkaline solution to form alkali activated binders. Attention was focused on the influence of the clay’s calcination treatment (450–500–600 °C) on the geopolymers’ microstructure of samples, remaining in the lower limit indicated by the literature for kaolinite or illite calcination. The mixtures of clay and alkali activators (NaOH 8M and Na-silicate) were cured at room temperature for 28 days. The influence of solid to liquid ratio in the mix formulation was also tested in terms of chemical stability measuring the pH and the ionic conductivity of the eluate after 24-h immersion time in water. The results reported values of ionic conductivity higher for samples made with untreated clay or with low temperature of calcination (≥756 mS/m) compared with values of samples made with calcined clay (292 mS/m). This result suggests that without a proper calcination of the as-received clay it was not possible to obtain 25 °C-consolidated AAMs with good chemical stability and dense microstructure. The measures of integrity test, pH, and ionic conductivity in water confirmed that the best sample is made with calcined clay at 600 °C, being similar (53% higher ionic conductivity of the eluate) or equal (integrity test and pH) to values recorded for the metakaolin-based geopolymer considered the reference material. These results were reflected in term of reticulation and morphology of samples through the analysis with scanning electron microscope (SEM) and X-ray diffraction (XRD), which show a dense and homogeneous microstructure predominantly amorphous with minor amounts of quartz, halloysite, and illite crystalline phases. Special attention was dedicated to this by-product to promote its use, given that kaolinite (and metakaolin), as primary mineral product, has a strong impact on the environment. The results obtained led us to consider this halloysite clay very interesting as an aluminosilicate precursor, and extensively deepening its properties and reactivity for the alkaline activation. In fact, the heart of this work is to study the possibility of reusing this by-product of an industrial process to obtain more sustainable high-performance binders.

Sustainable Chromium Encapsulation: Alkali Activation Route

“…In this paragraph we present the recent results proving the feasibility of low-cost aluminosilicate powder as base for the formulation of a geopolymer capable of encapsulating a large number of contaminants present in one real waste from the leather industry: Cr-bearing wastewater of the tannery process rich also in Cl 1and SO 4 2anions. The novel experimental results presented hereafter are related to one formulation where a clayey mining by-product (Sgarlata et al, 2022) totally replaced a commercial metakaolin (Argical ™ M1000, produced by Imerys, France) with quartz, muscovite/ illite, and anatase as principal crystalline phases and 55-59 wt% SiO 2 , 34-40 wt% Al 2 O 3 as major chemical constituents, D90 = 40 ± 2 µm (complete particle size distribution curves are presented in Supplementary Figure S1), and surface area = 18 ± 2 m 2 /g. The mining clayey by-product was the result of an efficient industrial waste recovery process for reuse as secondary raw materials mined in Lazio, in the province of Latina, Italy.…”

Effect of Magnesium Salt (MgCl2 and MgSO4) on the Microstructures and Properties of Ground Granulated Blast Furnace Slag (GGBFS)-Based Geopolymer

“…In addition, their manufacturing process consumes less energy and emits less CO 2 than the ordinary Portland cement (OPC) manufacturing process; thus, geopolymers have attracted considerable research attention and have been regarded as a potential alternative to OPC for preparing concrete materials [ 10 , 11 , 12 ]. Raw materials with sufficient amounts of reactive alumina and silica (such as clay minerals [ 13 , 14 ], solid waste [ 15 , 16 , 17 ], and other minerals [ 18 , 19 ]) and solid wastes such as mine tailings [ 17 , 20 ], fly ash (FA) [ 21 , 22 ], and slag [ 23 , 24 ] can be directly used as geopolymer precursors. In particular, finding use for solid waste in the concrete industry promotes environmental protection.…”