Minimising dust and slag to remove chloride, heavy metal(s) and salt(s) - by washing with organic acid, filtering and adding quicklime or slaked lime to solid to give hydraulic binder properties

摘要

Removal of chloride, heavy metals and their salts from dust and slag involves washing the starting material (I) in organic acid (II), filtering the mixt. and separate disposal of the filtrate and filter residue (III). The novelty is that, opt. after washing with water, (III) is treated with lime in the form of solid CaO or Ca(OH)2 suspension. (II) is pref. CH3COOH and/or HCOOH, CaO/Ca(OH)2 is added to give the end prodn. about the same CaO content as (I). In an example, incinerator slag had the following average heavy metal contents (cf. TVA permissible limits for inert materials) of 630 (500) ppm Cu, 860 (500) ppm Pb and 5400 (1000) ppm Zn and contained 8900 ppm Cl and 5-6% = 1 mole/kg of alkaline cpds., mainly CaO. The measured (permissible) concns. in the eluate were 0.4 (0.2) mg/l Cu, 0.2 (0.1) mg/l Pb and 4.7 (1.0) mg/l Zn. The slag was washed with 10 cu.m 1 M (II)/t slag, then filtered. The filtrate was recycled to the incinerator without further treatment. The concns. before/after washing were 672/438 ppm Cu, 796/230 ppm Pb, 1470/506 ppn Zn and 9770/6200 ppm Cl. The filter cake was treated with CaO/Ca(OH)2 to return its CaO content to ca. 5-6% and immobilise residual heavy metals. It was then suitable for building purposes, e.g. as cement for concrete mfr.