A certain gold mine processing plant originally had two independent grinding and flotation systems with capacities of 3000t/d and 800t/d. Later, to increase the gold production, it was decided to expand the 800t/d grinding and flotation system. After the expansion, this series achieved a daily processing capacity of 1400t/d.
The pre-expansion 800t/d series ore processing technology is as follows: the grinding process uses a single-stage grinding and classification process, with an MQG2736 grid-type mill and one FX-500 cyclone forming a closed-circuit grinding. The cyclone overflow enters the flotation operation, including one roughing and two scavenging, and the rough concentrate is integrated into the 3000t/d fine selection system.
The design principles for the 1400t/d series grinding system are:
(1) No impact on the original 3000t/d series. (2) Minimize equipment investment by utilizing the MQG2436 ball mill dismantled from other processing plants as the second-stage grinding equipment. (3) Considering the ore supply situation, achieve flexible conversion between this series and the original 800t/d series.
The process design aims to increase processing capacity based on the principles of speed, quality, and cost-effectiveness. The designed 1400t/d series process has an initial grinding particle size of no more than 13mm, accounting for 90% of the feed, and the product with a particle size of -0.074mm accounts for 55%.
The process uses an open-circuit for the first stage, employing one MQG2736 grid-type ball mill. For the second stage, a closed-circuit classification and grinding process is used, with one MQG2436 grid-type ball mill and two φ500mm cyclones. The overflow product enters the flotation operation.
After the expansion and modification, the plant failed to achieve the designed requirements despite multiple adjustments, and the production capacity was only around 1150t/d. Upon inspecting the grinding system and analyzing particle size screening results, the following conclusions were drawn:
The main reason for the low grinding processing capacity is that the first-stage grinding uses an open-circuit, limiting the full potential of the equipment. Open-circuit grinding results in an increased content of overground products, causing frequent blockages in the cyclone sand discharge port. Additionally, the low throughput of grinding causes severe wear of steel balls and liners, leading to excessive steel ball consumption. After studying the existing process, adjustments were made by adopting a two-stage two-closed-circuit process.
(1) Principles of Process Adjustment
a. The adjustment is made without making excessive changes to the original modified process. A two-stage two-closed-circuit grinding and classification process is adopted. The first-stage grinding and classification equipment uses the original 800t/d classification cyclone and ball mill to form a closed circuit, and the second-stage grinding and classification still uses the original modified equipment.
b. Allocation of grinding loads for the two stages. Referencing the original 3000t/d process, the circulating load rate for the first-stage grinding is controlled between 100% and 120%, and for the second-stage grinding, it is controlled between 150% and 200%.
c. Blockage issue in the first-stage grinding sand discharge. Due to the need to prevent large particles from entering the second-stage grinding while also performing appropriate coarse discharge, the originally designed first-stage grinding product with a particle size of -0.074mm accounted for 30%-35%. Using a conventional 20° cone-angle hydrocyclone proved difficult to meet the requirements, and the sand discharge port frequently got blocked, causing the grinding product to be coarse or overground at times, making debugging work impossible. It was decided to replace the original cone-angle hydrocyclone with a flat-bottom hydrocyclone to fundamentally solve the sand blockage problem.
(2) Process Debugging Steps
First, adjust the parameters of the first-stage grinding and classification to ensure that the first-stage grinding and classification hydrocyclone is not blocked and operates smoothly, with its overflow product free of large particles (+3mm). After the adjustment of the first-stage grinding system is completed, the second-stage grinding system is adjusted to ensure that its overflow product has a particle size of -0.074mm accounting for about 55%, and the hydrocyclone operates smoothly without any choking.
(3) Operating Results After Process Adjustment
After repeatedly changing the hydrocyclone parts specifications and more than a month of trial operation and debugging, the 1400t/d series of the processing plant under the direct ore dressing workshop smoothly reached production, and on March 4th, the processing capacity reached 1470t, with all indicators meeting the design requirements. After reaching full production, the concentration and fineness at various operation points are shown in the table below:
In this expansion and modification plan, replacing the cone-angle hydrocyclone with a flat-bottom hydrocyclone achieved the production requirements and solved the problems of hydrocyclone sand blockage and unreasonable load distribution for the two-stage grinding, realizing the successful application of hydrocyclones in the two-stage closed-circuit grinding and classification system.
