This article takes a low-grade feldspar ore as an example to describe the process of determining the beneficiation process flow, aiming to provide some possible ideas for processing low-grade feldspar ore.
Eight samples of the low-grade feldspar ore were selected for mineralogical identification under a microscope. Subsequently, four random samples were crushed, mixed, and homogenized for chemical multi-element analysis. The analysis results are shown in the figure below:
Research indicates that for the potassium feldspar ore in this area, it is difficult to achieve the desired concentrate specifications for feldspar and quartz separation under neutral conditions. Impurity minerals such as mica and tourmaline in the ore can be preferentially floated by adding a collector.
Therefore, when formulating the process flow, it is proposed to use flotation to remove impurity minerals. This approach can increase processing efficiency, ensure recovery rates, and simplify the process.
The proposed process flow schemes for the low-grade feldspar ore include:
Crushing - Grinding - Flotation (removing mica and tourmaline) - Magnetic separation.
Crushing - Grinding - Desliming - Flotation (removing mica and iron-bearing minerals) - Magnetic separation.
Crushing - Grinding - Desliming - Weak magnetic separation (removing iron) - Flotation (removing mica and iron-bearing minerals) - High-gradient magnetic separation.
Through comparative analysis and preliminary test results, the third scheme is preferred: crushing - grinding - desliming - weak magnetic separation (removing iron) - flotation (removing mica and tourmaline) - high-gradient magnetic separation. The following sections provide a detailed study of each stage of the process flow.
Crushing and Screening Process
Through crushing and screening experiments and analysis, it was determined that a three-stage crushing process should be used. If a double-layer screen is used for screening, it can reduce the mechanical load on the screening equipment compared to a single-layer screen, simplify the process, and reduce ore transport, but it may result in lower screening efficiency.
The ore extracted is first passed through a 300mm x 300mm grid screen, with large chunks of ore that remain on the screen manually crushed.
The coarse-crushed material from the grid screen is transported by a conveyor belt to a double-layer screen, which performs intermediate crushing.
The product from the intermediate crushing and the middle product from the double-layer screen are finely crushed together, with the finely crushed product returning to the double-layer screen for inspection and screening.
This setup constitutes a three-stage closed-circuit process.
The particle size distribution of the crushed ore is relatively uniform after crushing, with the dominant particle size ranging from 0.3-2mm, accounting for 59.07% of the feed. The yield of particles larger than 4mm is only 1.36%, while particles smaller than -0.074mm account for 12.96% of the total yield. This is partly due to the three-stage crushing process, which ensures thorough crushing of large ore chunks, and partly due to the ore's low susceptibility to crushing in this area.
Grinding and Classification Process
Based on experimental analysis, the grinding and classification process was determined to be a single-stage grinding process with classification.
The ore is directly fed into a ball mill, and the product after grinding is classified by a classifier, with most of the qualified particle sizes being separated, and unqualified particle sizes returning for regrinding in the ball mill.
The ball mill and classifier constitute a closed-loop operation. This configuration controls the maximum particle size of the qualified product and reduces the time the ore spends in the ball mill, avoiding over-grinding and increasing grinding efficiency.
Selecting a single-stage grinding process with classification is advantageous because it controls the maximum particle size while avoiding over-grinding, thus improving grinding efficiency.
Desliming Operation
Based on test results, it was found that desliming is more effective than not desliming. By desliming, the -0.038mm particle size fraction can be removed from the product, which contains a significant amount of iron-bearing minerals. As the diameter of the cyclone increases, the desliming rate gradually increases, but the concentrate specifications stabilize. Considering concentrate grade and yield, a 10cm-diameter cyclone was chosen as it provided better results, with a desliming rate of 5.55%.
Weak Magnetic Separation Process
During the crushing and grinding process, ore inevitably comes into contact with iron, which increases the iron content. For the glass and ceramic industry in this area, strict requirements are imposed on the iron content in potassium feldspar. Adding weak magnetic separation is primarily aimed at the iron-bearing minerals introduced during preparation operations. It can also remove some strongly magnetic minerals from the raw ore, reducing the cost of iron removal in the subsequent flotation process.
Weak magnetic separation reduced the iron content in the ore from 0.76% to 0.63%. The potassium-sodium (K2O+Na2O) grade remained stable. The tailings rate for weak magnetic separation was 3.58%, and the iron content in the tailings reached 4.06%.
Flotation Process
Numerous laboratory test results have shown that ideal concentrate specifications can be obtained by performing reverse flotation of impurity minerals. Therefore, the flotation section of the process used multiple impurity removal steps to achieve "enrichment of potassium and reduction of silicon" without the need to separate feldspar from quartz.
The chosen flotation flow employs a one-stage roughing and three-stage cleaning process in sequence, with middlings returning. The final concentrate undergoes high-gradient magnetic separation for iron removal.
The flotation concentrate specifications are as follows: yield 58.49%, K2O grade 8.94%, Na2O grade 3.59%, and iron content 0.33%.
High-Gradient Magnetic Separation
The flotation concentrate contains 8.94% K2O, 3.59% Na2O, and K2O+Na2O equals 12.53%, meeting the requirements for high-grade ceramic products. However, the concentrate contains 0.33% iron. To meet the requirement for Fe2O3 <0.15% in high-grade ceramic products, further iron removal through high-gradient magnetic separation is necessary.
The test results showed that as the intensity of the strong magnetic field increased, the yield of potassium feldspar concentrate decreased, and the iron content gradually decreased. When the magnetic field intensity was 1.2T, the iron content in the concentrate was 0.13%, meeting the requirements for high-grade ceramic products. Taking all factors into consideration, an appropriate magnetic field intensity of 1.2T was chosen for strong magnetic separation.
Through laboratory research and experiments on potassium feldspar ore in the area, a process flow consisting of three-stage crushing and screening, single-stage grinding with classification, desliming with a 10cm-diameter cyclone, weak magnetic separation for iron removal, one-stage roughing and three-stage cleaning flotation with middlings return, and high-gradient magnetic separation for final iron removal was determined to be the most suitable flotation process for the ore. This process does not require the use of hydrofluoric acid or sulfuric acid and is environmentally friendly, convenient to operate, and highly effective in "iron removal and silicon reduction."
