The Solidification of Lead-Zinc Smelting Slag through Bentonite Supported Alkali-Activated Slag Cementitious Material

Abstract

The proper disposal of Lead-Zinc Smelting Slag (LZSS) having toxic metals is a great challenge for a sustainable environment. In the present study, this challenge was overcome by its solidification/stabilization through alkali-activated cementitious material i.e., Blast Furnace Slag (BFS). The different parameters (water glass modulus, liquid-solid ratio and curing temperature) regarding strength development were optimized through single factor and orthogonal experiments. The LZSS was solidified in samples that had the highest compressive strength (after factor optimization) synthesized with (AASB) and without (AAS) bentonite as an adsorbent material. The results indicated that the highest compressive strength (AAS = 92.89MPa and AASB = 94.57MPa) was observed in samples which were prepared by using a water glass modulus of 1.4, liquid-solid ratio of 0.26 and a curing temperature of 25 °C. The leaching concentrations of Pb and Zn in both methods (sulfuric and nitric acid, and TCLP) had not exceeded the toxicity limits up to 70% addition of LZSS due to a higher compressive strength (>60 MPa) of AAS and AASB samples. While, leaching concentrations in AASB samples were lower than AAS. Conclusively, it was found that the solidification effect depends upon the composition of binder material, type of leaching extractant, nature and concentration of heavy metals in waste. The XRD, FTIR and SEM analyses confirmed that the solidification mechanism was carried out by both physical encapsulation and chemical fixation (dissolved into a crystal structure). Additionally, bentonite as an auxiliary additive significantly improved the solidification/stabilization of LZSS in AASB by enhancing the chemical adsorption capacity of heavy metals.

Assessment of Leaching Characteristics of Solidified Products Containing Secondary Alkaline Lead Slag

“…The base for Hfo formation was the iron from the slag (Table 2) [9,18]. It was noticed that the lead had small hydrated ions with high affinity towards physical adsorption, ion exchange, surface complexation, and precipitation [13]. Also, arsenate adsorption was related to the iron content of adsorbents and fitted by the Langmuir model by suggesting monolayer adsorption of arsenic onto adsorbents [35].…”

“…After 60 h of leaching, at pH 12, (Figure 4a), Pb release reached an equilibrium of 4.12 mg L −1 . According to the model, Pb exists predominantly in solution as hydroxide complexes (Pb(OH) 3 − and Pb(OH) 4 −2 ) (Table 9), due to its amorphous nature [13]. The negative SI values of Pb solid compounds (Table 10) indicate that the lead was soluble under this condition.…”

“…The management of lead slag is based on the prevention of the negative impact on the environment (decreasing toxicity) and favors a circular economy (increasing utilization) [5]. The S/S process is used for the treatment of lead slag with the toxic elements immobilization (physical encapsulation, adsorption, and ion exchange) in the geopolymer matrix [12] and with physical encapsulation and chemical fixation (dissolved into a crystal structure) in alkali-activated cementitious material [13]. The preferred technology to treat hazardous waste is metal recovery and reuse of the slag in construction materials [5].…”

Study on Solidification of Chromium-Containing Sludge With Alkali Slag Combined With Attapulgite

“…Kim et al (Kim et al 2005) combined slag and calcium oxide to treat the sludge and found that its mechanical properties are good, and it can meet the capping requirements of land lls. Mao (Mao et al 2019) uses bentonite as an additive to solidify lead-zinc smelting slag. Compared with using slag alone, its solidi cation effect and material properties are better.…”

A new expansion material used for roof-contacted filling based on smelting slag

“…Filling mining technology is a mining technology that uses filling materials to fill underground goaf. There are many kinds of filling materials, such as barren rocks, slags, tailings, cementitious material and cementitious material prepared with cement and the solid waste mentioned above in the land mines [1][2][3][4][5][6][7][8] . Moreover, the Sea sand and coral sand are also used in the Marine concrete engineering, especially in the reef construction in the open sea 9 .…”