Characterisation of iron-rich sludge: correlations between reactivity, density and structure

Abstract

This paper discusses the behaviour of iron-rich sludge, a problematic waste product of potable water treatment, minewater/groundwater management and hydrometallurgical processing. The work confirmed the highly hydrous and largely amorphous nature of the sludge and the significant differences that occur in reactivity (rate of acid leaching) and density (densification) depending variously upon the mode of sludge formation, pre-conditioning and storage. A structural study using a combination of FT-IR / ATR, XRD and TG/DTA correlated decreases in reactivity with ageing (i.e., with increases in particle size and/or degree of crystallinity) and increases in density with expulsion of weakly bonded water. The work underpinned studies on recycling of water treatment sludge with ion exchange resins and accelerated densification during sludge management.

Full‐Scale Removal of Arsenate and Chromate from Water Using a Limestone and Ochreous Sludge Mixture as a Low‐Cost Sorbent Material

“…Ochreous sludge is being generated continuously at water-supply facilities, when groundwater is aerated, to oxidize and precipitate its content of reduced iron, Fe(II), as Fe(III). The resulting Fe(III) oxides are primarily in the form of amorphous ferrihydrite, with a surface area of 100 to 350 m 2 /g (Georgaki et al, 2004;Jambor and Dutrizac, 1998). The sludge is highly hydrous, and the sludge dry matter consists of approximately 30 to 40% iron and sizeable concentrations of calcium, organic matter, silicic acid, phosphate, and quantities of trace elements representative for the groundwater source of origin (Aktor, 1990;Georgaki et al, 2004).…”

Treatment of Combined Sewer Overflows Using Ferrate (VI)

“…Iron occurs generally in two states, especially soluble ferrous iron and insoluble ferric iron (Vance, 1994). In sludge, iron is mostly present in amorphous form (Georgaki et al, 2004). The inavailability of exact speciation of iron in municipal sludges and variability of sludge composition have refrained researchers from using sludge as an iron source for generation of Fe (VI).…”

Research and evaluation of iron impact on sludge digestion process

“…When iron in water is presented in ferrous form (Fe 2+ ) ochre formates according to equations 1.14-1.16 (Усова et al 2011): Ochre usually contains over 70% of water in its structure; free water removal occurs via gravity sedimentation or flotation. Naturally dewatered ochre can contain up to 15% of solids; if ochre is dewatered mechanically, then total solids conent can be up 30% (Georgaki et al 2004).…”