Abstract
The potential possibility of blast furnace slag as a low-cost adsorbent to remove lead ions from wastewater was investigated in detail in the present work. Both single factor experiment and orthogonal experiment were performed to reveal the effect of pH, adsorption temperature, contact time and initial concentration of lead ions on the adsorption performance of pristine slag. In order to make clear the correlation between the lead ion adsorption performance and the structure of slag, solid state nuclear magnetic resonance (NMR) was conducted to reveal the network structure and X-ray fluorescence (XRF) was used to calculate the nonbridging oxygen in the network-forming tetrahedra. For the purpose of improving the adsorption performance, γ-aminopropyltriethoxysilane (APTES) was adopted to modify the slag via post-grafting method. The results show that the slag is predominately composed of SiO2, Al2O3, CaO and MgO, exhibiting an amorphous network structure based on SiO4 and AlO4 tetrahedra. The conditions for adsorption can be optimized as follows: a pH of 7, an adsorption temperature of 60 °C, a contact time of 120 min and an initial lead ion concentration of 40 mg·L−1. Under the optimal conditions, a removal rate of 99.98% and an adsorption capacity of 49.99 mg·g−1 are obtained for the pristine slag. The adsorption complies with the Langmuir model thermodynamically and conforms to the pseudo-second order model kinetically. It is noted that aminopropyl-modification has considerably enhanced the removal rate of lead ions from 20.71 to 64.32% and the adsorption capacity from 29.01 to 96.48 mg·g−1 since amino groups (-NH2) are more inclined to form a complex with lead ions than hydroxyl groups due to the higher nucleophilicity of amino groups than that of hydroxyl groups. However, it is necessary to develop more low-cost modification agents in the future work.
Highlights
As one of the most toxic and extremely hazardous heavy metals, lead causes serious damage to the kidney, liver, nervous, reproductive and gastrointestinal systems of humans [1,2]
The lead ion solution was prepared by dissolving a certain amount of Pb(NO3 )2 in deionized water
The slag is mainly composed of CaO, SiO2, Al2 O3 and MgO, accounting for more than 99% of the composition
Summary
As one of the most toxic and extremely hazardous heavy metals, lead causes serious damage to the kidney, liver, nervous, reproductive and gastrointestinal systems of humans [1,2]. Various techniques have been developed and employed for removing toxic heavy metal ions from wastewater, including but not limited to chemical precipitation [5], ion exchange [6], membrane separation [7], reverse osmosis [8], phytoremediation [9], adsorption [10,11,12,13,14], among others. Amongst these techniques, adsorption has received increasing attention due to its ease of operation and abundance of adsorbents [15,16,17]. Various industrial or agricultural wastes, for instance, sludge, blast furnace slag, flue dust, red mud, banana peel, soybean hull, spent coffee grounds etc., have been investigated for the adsorption of heavy metals from wastewater [14,17,19,20,21,22]
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