Alternative Method for the Treatment of Hydrometallurgical Arsenic–Calcium Residues: The Immobilization of Arsenic as Scorodite

Abstract

Arsenic−calcium residue (ACR) is one of the major hazardous solid wastes produced by the metallurgical industry that poses a serious threat to the environment. However, a suitable method for the effective treatment of ACR is still lacking. In this study, an alternative treatment method for ACRs via the immobilization of As as scorodite was proposed with the use of two types of ACRs (ACR real directly collected from a Pb refinery and ACR lab precipitated from waste sulfuric acid in the lab). The treatment of ACR included preparing the As-enriched solution via H 2 SO 4 dissolution−neutralization of ACR at pH < 2, As(III) was oxidized by H 2 O 2 , and As(V) was immobilized as scorodite. The results showed that gypsum produced from ACR lab in the dissolution− neutralization process contained 68 mg/kg of As, far below the Chinese national standard for hazardous solid wastes (<0.1 wt %, GB5085.62007). The gypsum produced from ACR real contained 5400 mg/kg of As due to the presence of original high-As gypsum (1.6 wt %) in ACR real . These results showed that the preliminary removal of SO 4 2− from waste sulfuric acid by lime neutralization− precipitation at pH ∼ 2 could produce pure-phase gypsum by avoiding the HAsO 4 2− isomorphic substitution for SO 4 2− . The scorodite produced from both ACRs displayed good As stability at pH 4.95 (0.9 and 0.5 mg/L) via the toxicity characteristic leaching procedure (TCLP) method and at pH 3−7 (0.4−3.0 mg/L) via a 15 day short-term stability test.

Separation and Stabilization of Arsenic from Lead Slime by the Combination of Acid Leaching and Forming Scorodite

“…Commonly used additives are divided into two kinds: inorganic additives, mainly including cement, volcanic ash, silicate and other materials, and organic additives such as thermoplastic materials, polymers and organic soil [13]. Solidification technology has shown great advantages in limiting the toxicity of polluting elements, but its applicability is poor due to the complex properties of slime and the diversity of curing product evaluation methods [14]. In the vitrification method, the Minerals 2021, 11, 1319 2 of 17 slime is mixed with glass matrix and heated to a melt state at high temperature, so that the slime is dissolved and then dispersed; thus, the resulting glass can show excellent chemical and biological inertia [15,16].…”

“…Traditional stabilization methods include the lime neutralization method and sulfide precipitation method [27]. The lime neutralization method refers to adding lime to arsenic-containing wastewater to generate calcium arsenite or calcium arsenate precipitate by adjusting pH value [14,28,29]. Note that calcium arsenate precipitates have high solubility under acidic conditions and will react with CO 2 dissolved in water to convert into calcium carbonate, leading to re-dissolution of arsenic [30,31].…”