Method for process water treatment

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.