The objective of flash flotation is to recover valuable minerals liberated during the primary grind. These valuable minerals are characterized for their high specific gravity and are recycled to the ball mill in a full scale operation. The hydrocyclone underflows transport the heavy particles, which are reground and its size is reduced. Flash flotation avoids the excessive overgrinding and reduces the losses of gold bearing minerals. The main purpose of the flotation tests is to obtain information on flotation kinetics and according to the results it is possible to decide the installation of a flash flotation cell in the primary grind circuit. The tests can be performed using a regular laboratory flotation machine such as Denver D-12 model. The flotation can be done on drill core samples or even from slurry samples obtained in full scale flotation plants. Probably, the second case is most sensitive and special care must be taken during the sampling.
It is important to take several samples from the hydrocyclone underflow and/or ball mill discharge for approximately one hour using an appropriate slurry cutter. Basically, the slurry sampled is poured into a 20 L bucket. Also, it is important to fill other bucket with process water. The first step is to perform wet screening at 600 microns. The oversize is separated and assayed for gold, silver, iron, copper and lead. The undersize is filtered and split in 2-kg charges that will be used to perform the flotation tests. All the tests must be done using process water and the lab flotation cell must have a volume of 2.5L.
The flotation reagents must be added in sequence and the conditioning time is extremely short, 15 to 20 sec. For this reason, the project metallurgist must provide a list of flotation reagents and the dosage. This information can be used from the operation; rougher flotation is the reference point. Once the condition is complete, the air valve is opened and the concentrate is collected at 15, 30, 60, 120, 180, 240 and 300 sec. It is important to set the flotation machine with the appropriate speed in order to promote good dispersion of particles, especially coarse particles. Once the test is complete, all products are filtered, dried, weighed and assayed for gold, silver, iron, copper and lead. The number of elements is determined with the information obtained in plant. Nevertheless, gold and silver are always included.
The final analysis is based on results from flotation kinetics test. The test is repeated several times in order to study the variability of the results. It is common practice to evaluate the results on samples obtained from different shifts due to mill operators tend to change operating parameters and the ore can be different in any aspect (e.g. gold content, mineralogy, interlocking).
Gold ore with high flotation rate