Mechanisms of lead, copper, and zinc retention by phosphate rock

Abstract

''Capsule'': Phosphate-induced formation of fluoropyromorphite is primarily responsible for Pb immobilization by phosphate rock, whereas Cu and Zn retention is mainly attributable to the surface adsorption or complexation. AbstractThe solideliquid interface reaction between phosphate rock (PR) and metals (Pb, Cu, and Zn) was studied. Phosphate rock has the highest affinity for Pb, followed by Cu and Zn, with sorption capacities of 138, 114, and 83.2 mmol/kg PR, respectively. In the PbeCueZn ternary system, competitive metal sorption occurred with sorption capacity reduction of 15.2%, 48.3%, and 75.6% for Pb, Cu, and Zn, respectively compared to the mono-metal systems. A fractional factorial design showed the interfering effect in the order of Pb O Cu O Zn. Desorption of Cu and Zn was sensitive to pH change, increasing with pH decline, whereas Pb desorption was decreased with a strongly acidic TCLP extracting solution (pH ¼ 2:93). The greatest stability of Pb retention by PR can be attributed to the formation of insoluble fluoropyromorphite [Pb 10 (PO 4 ) 6 F 2 ], which was primarily responsible for Pb immobilization (up to 78.3%), with less contribution from the surface adsorption or complexation (21.7%), compared to 74.5% for Cu and 95.7% for Zn. Solution pH reduction during metal retention and flow calorimetry analysis both supported the hypothesis of retention of Pb, Cu, and Zn by surface adsorption or complexation. Flow calorimetry indicated that Pb and Cu adsorption onto PR was exothermic, while Zn sorption was endothermic. Our research demonstrated that PR can effectively remove Pb from solutions, even in the presence of other heavy metals (e.g. Cu, Zn).

Repeatable use of wood ash to remove lead from contaminated water

“…Hence, the higher level of lead removal observed in this study is attributed to the low organic matter and the high calcite content. The level of lead removal by wood ash in this study is comparable to that by apatite, which is a high lead removal material [23][24][25] and is considerably higher than other industrial wastes [26]. The results suggest that wood ash from good combustion and low organic matter content can be useful as an effective lead removal material.…”

Trace Element Immobilization in Soil Using Amendments

“…Various sources of P have been tested for soil remediation purposes, including synthetic and natural phosphate minerals [120][121][122][123][124][125], phosphate-based salts (Na 2 HPO 4 , MgHPO 4 , (NH 4 ) 2 HPO 4 , 9Ca(H 2 PO 4 ) 2 [17,85,123,[125][126][127], phosphoric acid [122,[127][128][129][130][131][132], industrial by-products [17,86], biogenic phosphate (bone meal, bone char and ashes) [133,134] and their combinations in both laboratory and field experiments.…”

“…In soils amended with hydroxyapatite (HA), the main Pb immobilization mechanism is dissolution of HA followed by precipitation of highly stable hydroxypyromorphite, Ca 10Àx Pb x (PO 4 ) 6 (OH) 2 [117]. Similarly, addition of other apatite minerals or phosphate compounds can result in the formation of sparingly soluble pyromorphite-type minerals [Pb 10 (PO 4 ) 6 (F, Cl, B) 2 ], with precipitation dominating over surface sorption/complexation reactions [121]. The newly formed minerals have been demonstrated to significantly reduce Pb bioaccessibility and bioavailability [122,[135][136][137].…”

“…The competitive metal sorption was observed to reduce the binding capacity of hydroxyapatite for, for example, Pb, Cu and Zn when simultaneously present in the solution [118,121]. Addition of 0.2% of ammonium phosphate as a P source to soil resulted in a 12-and 3-fold increase in the concentration of dissolved Cu and Zn, respectively, even though the soil pH remained unchanged [17].…”

Pilot-scale Studies of Different Covers on Unoxidised Sulphide-rich Tailings in Northern Sweden: the Geochemistry of Leachate Waters

“…Hydroxyapatite has been shown to effectively immobilise heavy metals such as Cd, Zn, and Pb from contaminated waters and soils (Cao et al 2002;Cao et al 2004;Ma et al 1994;Singh et al 2001). Retention mechanisms are sorption, complexation, co-precipitation, or ion exchange (Cao et al 2002;Cao et al 2004;Chen et al 1997;Ma et al 1994;Mavropoulos et al 2002;Xu et al 1994).…”