Method for process water treatment
A method for treating process water of a flotation arrangement, the flotation arrangement including a flotation arrangement including a mineral flotation line and a process water treatment arrangement for treating underflow of the of the mineral flotation line. The method includes the steps of a) dewatering underflow from the flotation in a gravitational solid-liquid separator; b) subjecting supernatant from step a) to cleaning flotation for collecting at least fine particles and residual flotation chemicals, for separating at least fine particles and residual flotation chemicals from the supernatant into cleaning flotation overflow, and for forming purified process water as cleaning flotation underflow; c) removing cleaning flotation overflow as tailings, and d) recirculating purified process water into the mineral flotation line.
1 . A method for treating process water of a flotation arrangement comprising
a mineral flotation line comprising a first mineral flotation circuit for treating ore particles comprising valuable materials, the ore particles suspended in a first slurry, for the separation of the first slurry into a first mineral flotation circuit underflow and a first mineral flotation circuit overflow comprising a recovered first valuable material, and a second mineral flotation circuit arranged to receive the first mineral flotation circuit underflow as a second slurry infeed, for the separation of the second slurry infeed into a second mineral flotation circuit underflow and a second mineral flotation circuit overflow comprising a recovered second valuable material, and
a process water treatment arrangement for treating the second mineral flotation circuit underflow of the mineral flotation line; the method comprising the steps of:
a) dewatering the second mineral flotation circuit underflow in a gravitational solid-liquid separator to separate a sediment from a supernatant comprising water, residual flotation chemicals, fine particles, and microbes,
b) subjecting the supernatant to cleaning flotation, in which at least 90% of the flotation gas bubbles have a size from 0.2 to 250 μm, in a cleaning flotation unit for collecting at least fine particles and residual flotation chemicals, for separating at least fine particles and residual flotation chemicals from the supernatant into a cleaning flotation overflow, and for forming purified process water as a cleaning flotation underflow,
c) removing the cleaning flotation overflow as tailings, and
d) recirculating the purified process water into the mineral flotation line.
2 . The method according to claim 1 , wherein a first process water treatment arrangement is arranged to treat the second mineral flotation circuit underflow of the second mineral flotation circuit.
3 . The method according to claim 1 , wherein the first mineral flotation circuit is arranged to recover Cu, and the second mineral flotation circuit is arranged to recover Ni.
4 . The method according to claim 1 , wherein the mineral flotation line further comprises a third mineral flotation circuit arranged to receive the second mineral flotation circuit underflow as a third slurry infeed, for the separation of the third slurry infeed into a third mineral flotation circuit underflow and a third mineral flotation circuit overflow comprising a recovered third valuable material, and that the process water treatment arrangement is arranged to treat the third mineral flotation circuit underflow.
5 . The method according to claim 4 , wherein the first mineral flotation circuit is arranged to recover Cu, the second mineral flotation circuit is arranged to recover Ni, and the third mineral flotation circuit is arranged to recover sulphide.
6 . The method according to claim 4 , wherein the flotation arrangement comprises a first process water cleaning arrangement for treating the second mineral flotation circuit underflow of the second mineral flotation circuit and a second process water cleaning arrangement for treating the third mineral flotation circuit underflow of the third mineral flotation circuit.
7 . The method according to claim 6 , wherein a first cleaning flotation overflow of the first process water cleaning arrangement is directed to the third mineral flotation circuit as the third slurry infeed.
8 . The method according to claim 1 , wherein the cleaning flotation unit is a dissolved gas flotation (DAF) unit.
9 . The method according to claim 1 , wherein prior to step b), the temperature of the supernatant is 2 to 70° C.
10 . The method according to claim 1 , wherein prior to step b), the pH of the supernatant is 5 to 14.
11 . The method according to claim 1 , wherein in step a), the residence time of overflow in the gravitational solid-liquid separator is under 10 hours.
12 . The method according to claim 1 , wherein the solids content of the sediment of the gravitational solid-liquid separator is at least 80 w-%.
13 . The method according to claim 1 , wherein prior to step b), the supernatant is led into a separator overflow tank.
14 . The method according to claim 1 , wherein prior to step b), the supernatant is chemically conditioned by adding a coagulant and/or a flocculant and/or an additional flotation chemical.
15 . The method according to claim 14 , wherein the coagulant is chosen from a group comprising: bentonite, fixatives, aluminium salts, iron salts, polymer coagulants.
16 . The method according to claim 15 , wherein the coagulant is polyaluminium chloride (PAC).
17 . The method according to claim 16 , wherein the PAC is added into the supernatant in an amount of up to and including 500 ppm.
18 . The method according to claim 14 , wherein the supernatant is conditioned by adding the flocculant.
19 . The method according to claim 18 , wherein the flocculant is a polymer flocculant that is added into the supernatant in an amount up to and including 50 ppm.
20 . The method according to claim 14 , wherein the additional flotation chemical is chosen from a group comprising: collectors, activators, depressants, frothers, modifiers.
21 . The method according to claim 1 , wherein prior step d), water is subjected to filtration for removing compounds promoting microbiological growth.
22 . The method according to claim 21 , wherein in the filtration, a filtering unit comprising a ceramic filter is used.
23 . The method according to claim 1 , wherein at least 20% of the fine particles are removed from the second mineral flotation circuit overflow from the mineral flotation line.
24 . The method according to claim 1 , wherein at least 20% of the residual flotation chemicals are removed from the second mineral flotation circuit overflow of the mineral flotation line.
25 . The method according to claim 1 , wherein hardness of the purified process water is unaffected by the process water treatment arrangement.