A two-step pH control method to remove divalent metals from near-neutral mining and metallurgical waste drainages by inducing the formation of layered double hydroxide.

摘要: Abstract A neutral M2+-rich and M3+-poor (M = metal) metallurgical waste drainage was used to test a metal removal method based on the precipitation of layered double hydroxide (LDH). The LDH induced by adding salt Al3+ (trivalent missing in drainage) maintaining or restoring pH circum-neutral value. precipitates were characterized chemical analysis, XRD, ESEM, HRTEM XAS. main parameter controlling metals type precipitate appeared be pH. As function variation during experiments, analyses solutions showed either formation poor crystalline combined with very high Zn, Ni Pb (92–100%), more variable Mn (46–98%) less Cd (33–40%), lower Zn (62%), (43%), (88%), (64%) especially (1%). different efficiency two cases is only indirectly due crystallinity, it clearly affected following factors: 1) steps method; 2) direction within each step. In particular, highest obtained when first step goes towards acidic conditions, as consequence Al addition, quasi-amorphous hydrated hydroxysulfate (probably precursor felsӧbanyaite Al4(SO4)(OH)10 · 4H2O) occurs. This removes little no (just 0–3%) but essential so that second slightly alkaline NaOH can highly efficient removing divalent gradually turns into an incorporating Mg other metals. On contrary, both remain neutral-alkaline range, occurs observed. These results encourage further investigations inducing simple effective for treatment polluted drainages.