Sustainable solidification of ferrochrome slag through geopolymerisation: a look at the effect of curing time, type of activator and liquid solid ratio

Abstract

Ferrochrome (FeCr) slag was used as a precursor for the synthesis of a geopolymer. The effect of KOH concentration, liquid solid ratio (L/S), content of potassium metalisicate (KS) or potassium aluminate (KA), curing time on the unconfined compressive strength (UCS) and metal leachability of the synthesised geopolymer was investigated. A 10 M KOH and an L/S of 0.26 yielded a geopolymer with a UCS 13.0 MPa after 28 d of ambient temperature curing. A 0.125 wt KS:KOH addition yielded a geopolymer with a UCS of 14.7 MPa whilst a 1.25 wt KA:KOH addition yielded a geopolymer with a UCS of 24.5 MPa. The increase in strength was due to the formation of Calcium Silicate (Aluminate) hydrate. The aluminate activated FeCr slag geopolymer was the most competent of all geopolymers synthesised as it resulted in over 97% immobilisation of Fe, Zn, Mn, Ni and Cr. The 360-d static leachability tests for the aluminate activated geopolymer yielded a metal release rate lower than 90 mg mm − 2 of the geopolymer. The aluminate activated geopolymer also was resistant to changes in wet and dry cycles as it had a UCS reduction of 42% after 10 cycles whereas the pure FeCr slag geopolymer and the silicate activated geopolymer had a UCS reduction of 91 and 72% respectively after 10 cycles. The aluminate activated geopolymer met the minimum requirements for use as a paving brick for low traffic pavements. The study provides opportunities for sustainable use of FeCr slag with minimal environmental impact.

Influence of Ferrochrome Slag Co-Binder on Mechanical Behaviour of Fly Ash Geopolymer Mortars

“…It is known that FCS typically contains significant levels of chromium, which in turn is typically associated with adverse effects (Sections 1.0 and 2.0). Indeed, the observation of high chromium levels detected in the foregoing EDS analysis (Section 3.5.3), is consistent with reports given in the various literatures [9,10,25]. As mentioned earlier (Section 1.0), chromium in FCS could to some extent be potentially immobilised upon use of the slag as geopolymer precursor.…”

“…The uses of FCS include road construction works and making of refractory products. FCS contains chromium, thus its disposal in landfill sites poses environmental concerns arising from potential leaching of heavy metals and hazardous elements [9,10]. However, employment of FCS as an aluminosilicate material for producing geopolymer binders, could be environmentally beneficial, as the binder formation could to some extent immobilize hazardous elements.…”

Effect of Synthesis Conditions on Mechanical Strength of Aluminium Slag Modified Waste Foundry Sand Geopolymers

“…The highest UCS was recorded at 3M and was found to be 4.5 MPa. This was due to the rise in hydroxyl anions, contributing to the dissolution of species of silica and alumina [15]. However, when the concentration was increased 3 M, there was a sharp decrease in UCS.…”

Sodium Aluminate Activation of Non-ferrous Waste Foundry Sand: A Feasibility Study

“…The liquid-solid ratio less than 0.15 reduces the workability of the mixture, the paste was watery which reduces the hardening property of the brick. The decrease in UCS with increasing liquid-solid ratio is due to excess liquid which is not utilized during geopolymerisation and lost during the curing period, leaving voids that create a weak structure [9] . The UCS test conducted confirms that the sodium aluminate content was optimum at a liquid-solid ratio of 0.15.…”