Sorption of Ni(II) on surface of bed grains used in iron and manganese removal filters

Abstract

This paper reports the results of determinations of crystalline phase type, specific surface area, point of zero charge pH (pHpzc), and Ni(II) sorption capacities of beds for groundwater treatment. Bed materials from iron and manganese removal filters (FeRF, MnRF) as well as a catalytic bed (G1) were investigated. The reference material was MnO2-coated quartz sand (MnQS). The efficiency of Ni(II) sorption was investigated as a function of pH. It was found that the naturally formed coating on FeRF was characterised by the highest sorption efficiency (80–88%) in the wide pH range (4–9) of the solution. Sorption on MnRF was weaker (35–45%). G1 and MnQS, which contained only manganese oxides, were characterised by a very low sorption efficiency of 0–6% and 3–8%, respectively. A lower Ni(II) removal efficiency was observed at an initial pH close to the pHpzc values. During Ni(II) sorption, the pH of the solution was not constant and tended towards the value of pHpzc for all tested materials. The slightly pH-dependent sorption of Ni(II) indicates that its removal depends more on the chemical composition and the specific surface area of the oxide coatings covering the bed materials.

Mineral Materials Coated with and Consisting of MnOx—Characteristics and Application of Filter Media for Groundwater Treatment: A Review

“…It is known from other sources that Pyrolox contains ramsdellite, nsutite, and pyrolusite [204]. The specific surface area is not large: G-1 16.5 m 2 /g [144], Gabon manganese ore 7.25 m 2 /g [194], Pyrolox 2.58 m 2 /g [204].…”

“…Comparing adsorption capacities of coated filter media is also difficult because, although it significantly depends on the amount of oxide on the carrier grain and the size of the specific surface area, it is most often expressed in terms of the unit weight of the whole composite material. In chemically coated filter media, the carrier dominates quantitatively over the coating and it has been shown that for this type of materials it is better to compare adsorption capacity in terms of unitary value of specific surface area [144]. Bruins et al [145] considered this need when comparing filter media of varying density and proposed a reference to the unitary volume of material.…”

“…The increase of specific surface area of coatings obtained by the natural method can be very large, almost a hundred times larger compared to chemically coated quartz sand media, as well as coated media of other carriers (Table 2). Other sources indicate that the specific surface area of naturally coated sand formed for many years at groundwater treatment plant may be smaller and amount to 39.6 m 2 /g and 8.3 m 2 /g [144] for media from iron and manganese removal zones respectively. Media from top of filter bed removing iron, ammonium nitrogen and manganese after 3-year exploitation have increased their surface to 9.1 m 2 /g [179].…”

“…X-ray mapping analysis demonstrates the heterogeneous distribution of iron and manganese elements on the surface of naturally coated anthracite [167]. Media of both iron and manganese removal zones from groundwater treatment filters contain simultaneously iron and manganese [144,194]. The elemental composition of formed coatings identified at various groundwater treatment plants is presented in Table 6.…”

“…Mature coatings forming on naturally coated filter media are identified as poorly crystalline [183,194] and sometimes as entirely amorphous [197]. Contrarily, a large number of crystalline phases on the coatings of media from the iron and manganese removal filters were detected, what the authors explain by the fact that more than 10 years of ripening of the media resulted in the crystallization of iron and manganese oxyhydroxides [144]. Other authors have identified small and dense crystalline structures in the coatings, mixed with less dense, poorly crystalline or amorphous manganese oxyhydroxides [195].…”