A process for recovering metals such as Ni, Co, Mn, Cu, Zn, among others,
through precipitation as sulphides, enabling recovery of magnesium in the
form of hydroxide, carbonate and oxide and providing recovery of sulphate
as gypsum and ammonium sulphate. Liquid phase, after full treatment,
comprises recovered water with a quality proper for total reuse in
industrial process.
This process of liquid and solid effluent treatment is provided with
flexibility to process several types of effluents presenting wide
variations in their chemical composition. The main steps of this process
are: (1) equalization of liquid effluent, (2) precipitation of metals as
sulphides, (3) oxidation of metallic sulphides and crystallization as
metallic sulphates, (4) precipitation of magnesium as hydroxide and
calcination thereof into magnesium oxide (5) recovery of ammonia, (6)
preconcentration of the remaining saline solution, (7)
evaporation/crystallization of ammonium sulphate, (8) storage of
recovered water, (9) partial or total precipitation of sulphate contained
in the effluent with quicklime, (10) segregated storage of gypsum and
gypsum-magnesium mixture, (11) softening of the remaining solution and
(12) storage of softening water.