How to verify the separation effect of electromagnetic dry powder magnetic
separator?
Electromagnetic dry powder magnetic separator is the key equipment for
separating magnetic minerals and non-magnetic minerals in mineral processing
field, and its separation effect is directly related to the purity of finished
ore, subsequent processing efficiency and production benefit of enterprises.
Poor separation may lead to low recovery rate of magnetic minerals, magnetic
impurities mixed in non-magnetic minerals and other problems, affecting product
quality. Therefore, it is very important to scientifically verify the sorting
effect. The verification shall be carried out in multiple dimensions such as
finished product quality, sorting efficiency and equipment parameter
adaptability. Combined with specific detection methods and data judgment, the
following are detailed verification ideas and operating points.
1、 Starting from finished product quality: visual judgment of sorting
effect
The quality of the finished product is the most direct embodiment of the
sorting effect. It is necessary to focus on the two core indicators of "magnetic
mineral purity" and "residual magnetism of non-magnetic minerals", and draw a
conclusion through sampling inspection.
(1) Magnetic Mineral Purity Detection
The purity of magnetic minerals refers to the proportion of target magnetic
minerals in the magnetic products obtained after separation. The higher the
proportion, the better the separation effect is. The verification shall be
carried out according to the principle of "representative sampling": take
samples at the magnetic product outlet of the magnetic separator for several
times (no less than 5 times recommended) with the same sampling volume (e.g.
100g for every 10 minutes). Mix the samples evenly and then divide them into
appropriate amount (e.g. 200g for retention). Then, further purification shall
be carried out through the "magnetic separation tube method": put the samples
into the magnetic separation tube and carry out secondary magnetic separation
under the specific magnetic field intensity (similar to the operating magnetic
field of the equipment) to separate the non-magnetic impurities that may be
mixed in them. Weigh the sample mass before and after purification and calculate
the purity (purity=mass of magnetic minerals after purification/mass of original
magnetic product sample × 100%). If the purity meets the production requirements
(such as the required purity of an iron ore ≥ 95%), the separation effect of
this link is qualified; If it is lower than the standard, check whether it is
caused by insufficient magnetic field strength and fine non-magnetic mineral
particles.
In addition, it can be judged with the help of microscope observation: take a
small amount of magnetic product samples and observe them under the microscope.
Count the quantity proportion of non-magnetic impurities (such as gangue
particles). If there are few impurity particles in the field of view, it can
also prove that the purity meets the standard.
(2) Residual magnetism detection of non-magnetic minerals
Excessive residual magnetic minerals in non-magnetic minerals (i.e. tailings)
indicate incomplete separation and waste of resources. Take samples from the
outlet of the non-magnetic product during testing (the sampling method is the
same as that of the magnetic product), and divide the sample into two parts: one
is directly close to the sample with the "handheld magnetic detector", and
observe whether the instrument has magnetic response (the weaker the response
is, the less the residual is); The other is quantitatively detected by a
"magnetic analyzer" and the content of residual magnetic minerals is calculated
(usually the residual content is ≤ 1%, which is adjusted according to the
production standard). If the residual amount exceeds the standard, it may be
caused by the uneven magnetic field distribution of the magnetic separator and
the fast rotating speed of the roller, so that the magnetic minerals will be
discharged with the tailings in the future. The equipment parameters shall be
checked.
2、 Calculated by sorting efficiency: quantitative verification of resource
utilization
The separation efficiency is mainly reflected by the "recovery rate of
magnetic minerals", i.e. the proportion of magnetic minerals obtained after
separation to the total amount of magnetic minerals in the raw ore. The higher
the recovery rate is, the more sufficient the resource utilization is, the
better the separation effect is. The "Magnetic Mineral Content Test of Raw Ore
and Products" shall be completed before calculation, and the steps are as
follows:
First take the raw ore samples (take samples from the feed inlet of the
magnetic separator to ensure that they represent the overall characteristics of
the raw ore), remove the water with the "drying method" (avoid the impact of
water on weighing), and then conduct the full magnetic separation on the raw ore
samples through the magnetic separation tube to separate all the magnetic
minerals therein. Weigh the magnetic ore mass and the total mass of the raw ore
samples to obtain the magnetic mineral content of the raw ore (the magnetic rate
of the raw ore=the magnetic mineral mass in the raw ore/the total mass of the
raw ore samples × 100%).
Then, obtain the magnetic product sample according to the above method, test
the purity and quality of the magnetic mineral (record the output of the
magnetic product in unit time, such as 50kg per hour), and calculate the amount
of magnetic mineral actually recovered (actual recovery=hourly output of the
magnetic product × purity).
Finally, the recovery rate is calculated by the formula: recovery
rate=(actual recovery rate/(hourly processing capacity of raw ore × magnetic
rate of raw ore) × 100%. If the recovery rate reaches the preset target (such as
the recovery rate required by a beneficiation plant ≥ 90%), the separation
efficiency is qualified; If it is too low, check whether some magnetic minerals
are not adsorbed due to too much feeding, or the weak magnetic minerals cannot
be adsorbed due to insufficient magnetic field strength.
3、 Combined with equipment operating parameters: verify the suitability of
parameters and materials
The separation effect of electromagnetic dry powder magnetic separator is
closely related to the operating parameters. Unreasonable parameter setting will
lead to "fluctuation of separation effect". Therefore, parameter detection shall
be combined during verification to judge whether the parameters are suitable for
the material characteristics. Key parameters include magnetic field intensity,
roller speed and feeding amount. Specific verification methods are as
follows:
(1) Magnetic field intensity detection
Magnetic field intensity is the core power for absorbing magnetic minerals.
Gauss meter shall be used to measure the magnetic field intensity at different
positions on the roller surface (such as feed end, intermediate section and
discharge end), record the value and compare it with the rated value of
equipment. If the magnetic field intensity at a certain position is obviously
low (such as less than 10% of the rated value), it may be caused by the aging of
the electromagnetic coil and abnormal magnetization of the iron core, which will
affect the adsorption of the magnetic minerals in this area; Meanwhile, it shall
be judged according to the magnetic intensity of the material: if the weakly
magnetic mineral (such as hematite) is processed, the magnetic field intensity
shall reach 1500-2500 Gauss. If only 1000 Gauss is available at present, the
parameter shall be increased even if the value is stable.
(2) Verification of roller speed and feeding amount
The rotating speed of the roller determines the adsorption time of the
magnetic minerals in the magnetic field: if the rotating speed is too fast, the
magnetic minerals will be thrown out before they are completely absorbed;
Rotating speed is too slow, and non-magnetic minerals are easy to be suctioned
by mistake due to retention. During verification, samples can be taken at
different rotational speeds (for example, from 15r/min to 25r/min), and the
purity of magnetic products and tailings residue are compared to find the
optimal rotational speed of corresponding materials (for example, the rotational
speed can be slightly faster when processing coarse dry powder and slightly
slower when processing fine particles).
The feeding amount shall match the processing capacity of the equipment: too
much feeding, too thick material accumulation on the surface of the roller, and
the magnetic minerals at the bottom layer are difficult to be absorbed;
Excessive feeding and idling of equipment lead to waste of efficiency. The feed
rate can be changed by adjusting the feeder frequency, and the recovery rate of
magnetic products under different feed rates can be recorded. If the recovery
rate is the highest and stable under a certain feed rate, this parameter is
suitable.
4、 Long-term stability verification: ensure continuous compliance
The results of a single test may be influenced by occasional factors (e.g.,
transient material composition fluctuations), and the stability of the sorting
effect needs to be verified by "long-term monitoring". It is suggested to
continuously monitor for 72 hours, record the purity of magnetic products,
residual magnetism of tailings and equipment operation parameters every 2 hours,
and observe the trend after sorting out the data: if the fluctuation amplitude
of each indicator is ≤ 3% and all indicators are within the qualified range, it
indicates that the long-term separation effect of equipment is stable; In case
of obvious fluctuation (such as sudden decrease of purity in a certain period of
time), it is required to check whether there is abrasion of equipment parts
(such as change of magnetic field distribution caused by peeling of
wear-resistant layer on the roller surface), change of material characteristics
(such as sudden increase/decrease of magnetic rate of raw ore) and other
reasons, and re-check after timely adjustment.
Precautions during verification
The "representativeness" of sampling directly affects the verification
results, so it is necessary to avoid sampling at the edge of the outlet and
local accumulation, and uniformly sample and mix at the cross section of the
outlet; The inspection instrument shall be calibrated regularly (e.g. Gauss
meter shall be calibrated once a month) to avoid data distortion caused by
instrument error; The characteristics of different materials vary greatly (such
as magnetic intensity and particle size), so the verification method shall be
adjusted flexibly (such as fine particle dry powder sampling shall be sieved to
avoid agglomeration, and the magnetic field strength of weak magnetic minerals
shall be mainly inspected to see whether it is sufficient).
In a word, the separation effect verification of electromagnetic dry powder
magnetic separator shall be carried out in combination with multi-dimensional
"finished product quality, separation efficiency, parameter adaptability and
long-term stability". Through scientific sampling, accurate detection and data
comparison, it can not only judge whether the current separation effect meets
the standard, but also provide basis for equipment parameter optimization and
troubleshooting, and finally guarantee the quality and efficiency of mineral
processing.