Test Summary of Collectors for Silica Removal by Reverse Flotation of Phosphate Ore
1. Test Background and Objectives
As the fundamental raw material for phosphorus chemical industry, the quality of phosphate ore directly affects the quality and production cost of downstream products. Reverse‑flotation silica removal is a critical process to upgrade phosphate‑ore grade. It achieves efficient separation of phosphorus and silicon by selectively collecting silicate minerals and depressing phosphate minerals. This test is intended to screen and optimize collectors applicable to the process from. It focuses on investigating silica‑removal efficiency, phosphorus loss rate, reagent cost and process adaptability of different reagents, so as to provide data support for industrial‑scale application.
2. Test Methods and Conditions
Test Raw Ore
Low‑grade phosphate ore obtained from a mine (run‑of‑mine P₂O₅ grade: 22%‑25 %, SiO₂ content: 15 %‑18 %) was crushed and ground, with over 85 % of particles passing 0.074 mm sieve, and the ground ore was taken as flotation feed.
Test Reagents
Five types of collectors were compared in the test:
Fatty‑amine‑based collectors: coco diamine, dodecylamine, coco amine
Ether‑amine‑based collectors: C10 ether‑amine, isodecyl ether‑amine
Amine‑ether‑based collector: coco‑amine polyoxyethylene ether
Amine‑oxide‑based collector: cocamidopropyl amine‑oxide
Blended reagent systems: coco diamine mixed with fuel oil at 1:1 ratio; C10 ether‑amine mixed with oxidized paraffin soap at 2:1 ratio
Test Flow
A "one‑roughing and one‑cleaning" reverse‑flotation flow was adopted. Pulp pH was fixed at 5.5 and adjusted with sulfuric acid. Starch was used as depressant at a dosage of 1.5 kg/t. Collector dosages were set in gradient from 0.3 kg/t to 1.2 kg/t. Flotation duration was 4 minutes for roughing stage and 3 minutes for cleaning stage.
3. Test Results and Analysis
(1) Single‑collector Test Results
Coco diamine: At the dosage of 0.6 kg/t, it reaches a silica removal rate of 51.5 %, phosphorus loss rate of 8.2 %, and concentrate P₂O₅ grade of 30.4 %.
Dodecylamine: At the dosage of 0.6 kg/t, it reaches a silica removal rate of 38.7 %, phosphorus loss rate of 12.5 %, and concentrate P₂O₅ grade of 28.1 %.
C10 ether‑amine: At the dosage of 0.75 kg/t, it reaches a silica removal rate of 60.2 %, phosphorus loss rate of 15.3 %, and concentrate P₂O₅ grade of 29.8 %.
Coco‑amine polyoxyethylene ether: At the dosage of 0.6 kg/t, it reaches a silica removal rate of 45.3 %, phosphorus loss rate of 10.1 %, and concentrate P₂O₅ grade of 29.1 %.
Cocamidopropyl amine‑oxide: At the dosage of 0.6 kg/t, it reaches a silica removal rate of 32.1 %, phosphorus loss rate of 18.7 %, and concentrate P₂O₅ grade of 26.5 %.
Key conclusions:
Coco diamine shows the best comprehensive performance. It achieves 51.5 % silica removal rate with merely 8.2 % phosphorus loss rate, and lifts concentrate P₂O₅ grade up to 30.4 %, which meets industrial technical indicators.
C10 ether‑amine delivers the highest silica removal rate of 60.2 %, but its phosphorus loss rate is obviously higher than coco diamine; hence further optimization by blending is required.
Amine‑oxide‑based reagent presents poor performance and excessively high phosphorus loss rate, so it is not suitable for independent use.
(2) Blended‑system Test Results
Blended system of coco diamine and fuel oil (1:1): silica removal rate 58.7 %, phosphorus loss rate 9.5 %, concentrate P₂O₅ grade 31.2 %, reagent cost 120 CNY per ton ore.
Blended system of C10 ether‑amine and oxidized paraffin soap (2:1): silica removal rate 63.1 %, phosphorus loss rate 12.8 %, concentrate P₂O₅ grade 30.5 %, reagent cost 105 CNY per ton ore.
Key conclusions:
Blended systems can significantly improve silica‑removal performance. The system of coco diamine plus fuel oil raises silica removal rate to 58.7 % while keeping phosphorus loss rate under control at 9.5 %.
Although the blended C10 ether‑amine system obtains an even higher silica removal rate of 63.1 %, its phosphorus loss rate remains relatively high, which calls for further adjustment of blending ratios.
Reagent cost of blended systems increases by 10 %‑20 % compared with single reagents. Nevertheless, such cost increment can be offset by lower reagent consumption or higher concentrate grade.
4. Mechanism Analysis
Dominant Mechanism of Coco Diamine
Molecules of coco diamine contain two amino groups and mixed carbon‑chain structures. The combined effect of physical adsorption and chemical interaction strengthens its selective adsorption on quartz surfaces. Besides, its hydrophobic carbon‑chains can effectively disperse ore slime and reduce entrainment loss of phosphate minerals.
Synergistic Mechanism of Blended Systems
Fuel oil lowers pulp surface tension and facilitates the spreading of coco diamine across mineral surfaces. Oxidized paraffin‑soap improves the dispersibility of C10 ether‑amine through emulsification, and enhances its collecting capacity for silicate minerals.
5. Suggestions for Industrial Application
Preferred reagent: Coco diamine is recommended as the main collector for its high silica‑removal efficiency, low phosphorus loss rate and good process adaptability.
Optimization by blending: For high‑silicon silico‑calcareous phosphate ore, adopt the blended system of coco diamine and fuel oil at 1:1 ratio to further reduce phosphorus loss.
Process control suggestions: Pulp pH shall be maintained at 5.0‑5.5, starch depressant dosage at 1.5 kg/t, and flotation temperature kept within 25‑30 ℃ to acquire optimal separation results.
Economic assessment: The unit cost of coco diamine as single reagent is around 100 CNY per ton ore, and the cost rises to 120 CNY per ton ore for blended system. However, the upgraded concentrate grade can greatly cut downstream processing costs and bring prominent comprehensive economic benefits.
6. Conclusions
This test proves that coco diamine and its blended systems perform excellently in silica removal by reverse flotation of phosphate ore, and realize the balance between high‑efficiency silica removal and low phosphorus loss. Future research can focus on the development of green reagents (such as improving biodegradability) and intelligent flotation control technologies, so as to further enhance the economy and environmental‑friendliness of the whole process.