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Effectiveness of fly ash on the stabilization/solidification of Zn-contaminated soil

Chen Yan, Zhu Shengyuan, Fang Wei, Huang He, Qin Hao, Hu Shengtao, Wu Yuzhao

Environment Protection Engineering

2023

Vol. 49, nr 3

15--29

As a solid waste, the associated disposal cost of fly ash is really high. Previous studies suggested that the utilization of fly ash to treat heavy metal-contaminated soils was a new cost-effective method of disposal of it. Therefore, the effectiveness of fly ash stabilized/solidified Zn-contaminated soils has been investigated by unconfined compressive strength (UCS) and toxicity characteristics leaching procedure (TCLP) tests. Quantitative analysis of the soil microstructure was conducted by processing the X-ray diffraction (XRD) and scanning electron microscope (SEM) images. Mercury intrusion porosimetry (MIP) was carried out to illustrate the size and proportion of pore size for specimens under different ratios. The results of the tests showed an improvement in the UCS, which further increased as the content of binders was raised. Binder content would have little influence on the development of strength if the binder content exceeds a threshold value. The leached Zn2+ concentration of stabilized specimens was significantly decreased compared to that of untreated. Quantitative analysis confirmed that the addition of the binders resulted in the amount of hydration product, reduction of porosity, and a really random pores orientation, which was responsible for the improvement of the strength and leaching properties of the Zn2+ contaminated soils.

Direct hydrometallurgical separation of Zn(II) from brine leaching solution of zinc filter cake by simple solvent extraction process

Balesini-Aghdam Ali-Asghar, Yoozbashizadeh Hossein, Moghaddam Javad

Physicochemical Problems of Mineral Processing

2019

Vol. 55, iss. 3

667--678

The zinc leaching filter cake residue as a secondary resource is used for hydrometallurgical lead production from brine (chloride) media. In this method, zinc accumulation caused decrease in the lead leaching efficiency in feed solution as well as a defective cycle flowsheet in production process. Therefore, an experiment was designed for the solvent extraction (SX) of zinc from brine solution after lead cementation stage. The results indicated that approximately 98% zinc with a little contamination of other metals was extracted under optimum conditions (193.5 g.dm-3 of D2EHPA in kerosene as diluent, pH=3.5, contact time=5 min, temperature=40±2 °C and aqueous: organic ratio (A:O)=1:1). Also, according to the differences of ∆pH0.5 and separation factor values among Zn and other ions, D2EHPA as an organophosphorous extractant has suitable capability for zinc selective extraction from brine solution. Moreover, H2SO4 solution which was used for stripping to transfer Zn2+ ions to zinc conventional production sulphate media achieved high efficiency of 99%. McCabe-Thiele diagram was simulated to counter-current extraction route. The results showed that two stages were needed for both extraction and stripping.

Study of Complex Formation Between 18-Crown-6 with Cu2+, Zn2+, Cd2+ and Pb2+ Cations in Some Binary Mixed Non-aqueous Solvents Using the Conductometric Method

Rounaghi G., Khazaee N., Sanavi K.

Polish Journal of Chemistry

2005

Vol. 79 / nr 7

1143-1153

The complexation reactions between Cu2+, Zn2+, Cd2+ and Pb2+ metal cations with 18-crown-6 (18C6) were studied in methanol (MeOH) - dimethylformamide (DMF) and ethylacetate (EtOAc) - dimethylformamide (DMF) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complexes in all cases is 1:1 (ML). The values of thermodynamic parameters ( Hc 0, Sc 0) for 18C6-Cu2+, 18C6-Zn2+, 18C6-Cd2+ and 18C6-Pb2+ complexes in MeOH - DMF and EtOAc - DMF binary systems were obtained from temperature dependence of stability constants. The results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents and in most cases, the complexes are enthalpy stabilized but entropy destabilized. The stability constants Kf of all complexes increase with increasing the concentration of solvent with lower donicity (based on Gutmann donicity scale) in the binary mixed solvents. In most cases, a non-linear behaviour was observed for variation of logKf of the complexes with the composition of the mixed solvents. The selectivity order of 18C6 for these metal cations in all solvent systems used in this study is: Pb2+>Cd2+>Cu2+>Zn2+.