Recovery Process from Sedar report on AMY
The proposed processing plant is designed to process mill feed containing 2.2% to
3.5% Mn in the range of 3,500 t/d to 7,000 t/d, to produce 50,000 t/a of EMM at a
purity of higher than 99.7% Mn and an overall recovery of 88 to 93% Mn. Anhydrous
sodium sulphate will be produced as a byproduct.
The ROM mill feed will be trucked from the open pit to the crushing facility located at
the plant site. Two stages of crushing will reduce the ROM feed to a particle size of
100% passing 5 mm. The first stage of the crushing will use a sizer crusher in an
open circuit. The second stage of crushing will use an impact crusher in a closed
circuit with a dry screen. The product from the crushing circuit will be stored in two
7,000-t fine ore surge bins prior to being conveyed to the leaching circuit.
The crushed mill feed will be leached in two stages: pre-conditioning leaching with
acidic solution containing sulphuric acid (mainly recycled from downstream washing
circuits), and sulphur dioxide reductive leaching. The insoluble manganese in the 4+
oxidation state can be readily reduced to the soluble 2+ oxidation state by adding
sulphur dioxide. Both leaching agents—sulphur dioxide and sulphuric acid—will be
generated from burned liquid sulphur on-site.
The leached slurry after aeration will be directed to the counter-current decantation
(CCD) circuit, where the manganese-bearing pregnant leach solution (PLS) will be
separated from the leach residue. The leach residue will be subjected to multiple
stages of CCD washing, followed by further dewatering in pressure filters to reduce
water consumption and water content of the residue for waste rock/residue co-
deposit. The washed leach residue will be back-hauled by truck to the excavated
area within the open pit and blended for co-disposal with waste rock.
The PLS will be treated by two stages of purification to remove any impurities (such
as iron, aluminum, zinc, nickel, etc.) which may have detrimental effects on the
downstream operations.
The purified PLS containing mainly manganese sulphate and manganese dithionate
is directed to the manganese carbonate precipitation circuit. The precipitation of
manganese carbonate is achieved by mixing the purified PLS with sodium carbonate.
In the precipitation process, soluble sodium sulphate and sodium dithionate are
effectively eliminated from the manganese carbonate product. The resulting
manganese carbonate precipitate will then be separated from the solution by
thickening and filtration. The sodium sulphate and sodium dithionate solution will be
sent to the nanofiltration/ mechanical vapour recompression (MVR) evaporation
system to recover sodium sulphate and water.
The manganese carbonate solids will be dissolved by the acidic spent electrolyte
solution produced from the manganese electrowinning circuit. This solution is further
purified in two stages to remove any impurities and to generate the manganese
electrolyte feed for subsequent use in the EMM electrowinning process.
The electrolyte feed (neutral manganese sulphate) will be pumped into the
electrowinning cells where the anode and cathode compartments are separated by
semi-permeable diaphragms. At the cathode, Mn2+ will be reduced to Mno(s) and
deposited onto the cathode plate. Depending on process conditions, cathodic
hydrogen gas and anodic oxygen or manganese dioxide will be generated,
respectively, due to competing side reactions.
Manganese metal obtained at the steel cathode plates will have an overall purity of
over 99.7% Mn. The deposited manganese will be treated by washing and
passivation prior to being peeled from the cathode plate. The manganese metal
flakes will be transported to the manganese stock silo, and then bagged for
shipment.
Sedar report explains Recovery Method
The sodium sulphate and sodium dithionate solution from the manganese carbonate
precipitation circuit will be further processed to recover the sodium sulphate
produced as a byproduct and water, which will be reused as process water.
The heat generated from the liquid sulphur burner will be recovered and used to
generate electricity by a steam turbine, and/or provide direct heating in the form of
intermediate steam, as needed in the process.
