Use of granular slag columns for lead removal

doi:10.1016/S0043-1354(02)00120-3

Water Research

Volume 36, Issue 16, September 2002, Pages 4001-4008

https://doi.org/10.1016/S0043-1354(02)00120-3 Get rights and content

Abstract

The use of granular blast furnace slag (GBFS)-packed columns to treat lead-containing solutions has been investigated. The results obtained indicated that the slag usage rate decreased with increasing flow velocity, particle size, initial lead concentration and decreasing with bed height. Lead removed selectively in the presence of other heavy metal ions. High concentrations of sodium and especially calcium in the solutions impeded the uptake of lead. For 20 mg l⁻¹ lead concentration an empty bed contact time greater of 4 min provided to efficient use of the slag bed. Column pH was an important parameter to lead removal under dynamic conditions and reflected the influence of the investigated factors. During all runs lead breakthrough coincided with an abrupt drop in effluent pH. The apparent mechanisms of lead removal in GBFS column are sorption (ion exchange and adsorption) on the slag surface and precipitation.

Introduction

Lead has a specific toxic and cumulative effect and its discharge into environmental represents serious threat to many life forms. Industrial waters from battery manufacturing, metallurgy, metal finishing, chemical industry, etc., belong to the main Pb pollution sources. Lead in these waters should be reduced to levels in correspondence to the rules of regulatory agencies. The usual method for removal of lead is chemical precipitation [1], [2]. Sorption processes including ion exchange and adsorption are an alternative with great potential to treat water and wastewaters containing heavy metals [3], [4]. The main disadvantage of the sorption method consists in the high price of the adsorbents, which increases the price of the wastewater treatment. The search of inexpensive adsorbents, especially, such as by-products and waste from various industries has been the purpose of many investigators [5], [6], [7], [8], [9], [10]. Some of these materials combine good adsorption capacities and buffering effect, which assure almost complete removal of heavy metal ions without preliminary correction of the initial pH being necessary.

Blast furnace slags from ferrous metallurgy are complex mixtures of alkali-earth silicates and aluminosilicates formed at high temperatures in the blast furnace. Earlier research [11], [12] has shown that the blast furnace slag is a good adsorbent towards copper, zinc, nickel and lead ions. Granulated blast furnace slag also has a suitable particle size and good filtering properties.

The alkali or buffering effect of blast furnace slags in aqueous solutions determines some peculiarities of the process of elimination of heavy metal ions and is one of the reasons for which the mechanism of the process cannot be defined explicitly. It is known that heavy metal adsorption is effective in an alkaline region. However, when the medium pH is controlled by the adsorbent (as in the cases of various alkali and alkali-earth silicates), the mechanism of heavy metals removal is difficult to determine. According to Dushina and Aleskovaski [13], the ion exchange is a first step of metal ion detention on the surface of various calcium silicate materials, including slags. Depending on the nature of the material and the conditions of the experiment, the process may continue with further interactions between the metal ions and the solid matrix. The formation of sparingly soluble compounds of the type of metal silicates (surface precipitation) is possible. Yamashita et al. [14] have reported that the mechanism of adsorbing and fixing heavy metals of the converter furnace slag can be attributed to one or more of following effects: adsorption, coprecipitation, hydroxide precipitation as hydroxide, sulphide and ion exchange.

If the blast furnace slag is considered as a method for heavy metal removal, it is necessary to carry out a detailed research of its efficiency in a column process. The aim of this study was to establish the possibility of using granular blast furnace slag (GBFS) columns for treating waters containing heavy metal ions. Lead was chosen as a representative of the heavy metals as one of the most widespread pollutants and, besides, has already been investigated in batch-type contact process. The main task of the study was to determine the effectiveness of the lead removal process in GBFS column depending on influent pH and metal ion concentration, particle size, bed contact time, flow velocity, etc.

Section snippets

Materials and methods

The GBFS used was a commercial product of the Kremikovtsi JSC in Bulgaria. Its chemical composition (as oxides in wt%) was Na₂O—1.6, K₂O—1.9, CaO—44, MgO—3.2, BaO—3.5, SiO₂—34, Al₂O₃—6.4, MnO—2.4, Fe₂O₃—0.5, TiO₂—0.4 and S—1.7. The X-ray spectra of the slag showed no peak, which indicated an amorphous structure. The specific surface area determined by the N₂ BET method was 1 m² g⁻¹. GBFS was fractionated, rinsed with distilled water to remove fines, dried at 105°C and stored in a bank.

All working

pH of GBFS column

In order to examine the alkaline effect of the GBFS in a column, a separate set of column experiments were carried out with an influent without Pb (I=0.01 M, initial pH and Ca concentration 4.0 and 1.85 mg l⁻¹, respectively). Fig. 1 shows the effluent pH and Ca concentration during the run. Relatively high and constant effluent pH values (9.2–8.9) were observed in the range 27–240 BV, after which the effluent pH dropped sharply. The calcium effluent concentration also changed. The initial increase

Conclusions

The paper contains results from a laboratory investigation on the removal of heavy metal ions from water solutions by granular slag. The effect of pH, lead concentration, competing metal ions, slag particle size, flow velocity and contact time on the removal of lead in a column has been studied. The column pH reflects a complex effect of the different factors and it is an indicator of the column performance. Lead breakthrough and abrupt drop of effluent pH occurred simultaneously. The obtained

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Use of granular slag columns for lead removal

Abstract

Introduction

Section snippets

Materials and methods

pH of GBFS column

Conclusions

Water Res

Water Res

Water Res

Water Res

Industrial wastewater treatment technology

Removing lead from wastewater using zeolites

Water Environ Technol

Removal of toxic metal ions from solutions using industrial solid byproducts

Water Res