Abstract
Steel slag, which makes up a gigantic amount of metallurgical industrial solid waste, was in this experiment successfully synthesized an inexpensive adsorbent used to remove nitrate pollution from aqueous solution. This adsorbent was obtained by mixing steel slag, aluminium hydroxide and deionized water, and aging this at a mass ratio of 3:0.45:2, and then activating it at 800 °C. The physicochemical characteristics of the steel slag before and after modification were investigated to compare the effect of their surface properties on the adsorption behaviour of nitrate. The effects of adsorbent dosage, pH, and contact time on the adsorption process were investigated. The results showed that an increase in specific surface area and the formation of a positive surface of the modified steel slag (MSS) compared with the original steel slag (OSS) could effectively increase the number of the active adsorption sites and nitrate removal ability. The optimum parameters for nitrate removal were as follows: the concentration of nitrate was 20 mg/L, the dosage was 1 g/100 mL, the pH was four, and the reaction time was 180 min. The adsorption capacity of the MSS was approximately 1.9 times that of the OSS. The nitrate adsorption of the MSS was in accordance with the pseudo-second-order model and the Freundlich model, which indicated that the adsorption of nitrate on the MSS was mainly single layer chemical adsorption. The mechanism of nitrate removal mainly included ion exchange, hydrogen bonding, electrostatic interactions and intermolecular interactions. In addition, regeneration experiments indicated that the MSS after regeneration still had the capacity to remove nitrate.
Highlights
Nowadays, large areas of surface and groundwater are exposed to the risk of nitrate contamination in various countries and regions
The filters were packed on a vacuum filter, the leachate was collected by filtration and the concentrations of copper, zinc, lead, chromium, vanadium and arsenic leached from steel slag before and after modification were measured
After the analysis of the final nitrate content of each filtrate, the highest adsorption efficiency appeared in the MSS13, which mass ratio of steel slag, deionized water and Al(OH)3 was 3: 2: 0.45, and the calcination temperature was 800 ◦ C
Summary
Large areas of surface and groundwater are exposed to the risk of nitrate contamination in various countries and regions. Many materials, such as activated carbon, sepiolite, chitosan and ion exchange resin [8,10,11,12] can remove nitrate in water, but most of these compounds have high production costs, complex synthesis processes or are difficult to regenerate They are not suitable for the treatment of large areas of nitrate-contaminated water. It has a loose and porous structure, high density, settles fast in water, a short cycle of solid–liquid separation, and contains alkaline oxide and a large amount of iron and silicon These features make steel slag a possibility for the adsorption of pollutants in wastewater [14]. It has been found that this modification method could improve the nitrate removal efficiency by enlarging the porosity and surface properties, the amount of active substances and the positive charge on the surface of the steel slag to a large extent
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