In mining flotation, sodium carboxymethyl cellulose (CMC) is often used as an inhibitor of gangue minerals (such as quartz, feldspar, silicate, etc.), which separates useful minerals from gangue by adsorbing on the surface of gangue to form a hydration film or hindering the adsorption of collectors. The selection of its indicators needs to be combined with the properties of the ore, the flotation target and the slurry environment, and the core revolves around the four principles of inhibition efficiency, selectivity, stability and operational adaptability. The following is the selection logic and basis of key indicators:
1. Basis for the selection of core performance indicators
1.1 Degree of substitution (DS): Determines adsorption selectivity and water solubility
The degree of substitution (DS) is the average number of carboxymethyl groups (-CH₂COONa) replaced by each glucose unit in the CMC molecule (usually in the range of 0.5~1.2), which is the core indicator affecting the performance of CMC.
Mechanism of action: The degree of substitution directly affects the water solubility, charge density and adsorption capacity of CMC on the mineral surface. The higher the DS, the more carboxyl groups (-COO⁻) in the molecule, the better the water solubility (completely soluble when DS≥0.6), and the higher the negative charge density, the easier it is to adsorb on the surface of gangue minerals (such as silicate minerals such as quartz and feldspar) through electrostatic attraction or hydrogen bonding.
Selection principles:
If the surface of the gangue mineral is weakly positively charged or there are metal ion sites (such as calcium and magnesium gangue), a higher DS (0.8~1.2) is required to enhance the negative charge density and strengthen the inhibition through electrostatic adsorption or chelation;
If the gangue is easy to mud (such as fine-grained quartz), a medium DS (0.6~0.8) is required to balance water solubility and selectivity to avoid excessive adsorption and inhibition of useful minerals;
CMC with low DS (<0.6) has poor water solubility and is easy to agglomerate, which is only suitable for simple ores or low-dosage scenarios.
1.2 Molecular weight (viscosity): regulating inhibition strength and pulp fluidity
The molecular weight of CMC is positively correlated with the viscosity of its aqueous solution (usually expressed as 2% aqueous solution viscosity, ranging from 5 to 1000 mPa·s), which directly affects the inhibition strength and pulp operating performance.
Mechanism of action: The higher the molecular weight, the longer the molecular chain, the thicker the hydration film formed after adsorption on the gangue surface, and the stronger the inhibition effect; but high viscosity will increase the viscosity of the pulp, causing the flotation foam to become sticky, the fluidity to decrease, and even affect the floating of useful minerals.
Selection principles:
For coarse-grained gangue or difficult-to-inhibit gangue (such as iron-containing silicates), high viscosity (500~1000 mPa·s) is required to enhance inhibition through thick hydration film;
For fine-grained muddy gangue or easy-to-float gangue, medium-low viscosity (50~500 mPa·s) is required to avoid high viscosity of the slurry and difficulty in sorting;
When flotating ores with high fine mud content, low viscosity (<50 mPa·s) is preferred to ensure that CMC is quickly dispersed and evenly covers the surface of the fine mud.
1.3 Purity: Reduce impurity interference.
The purity of CMC (usually expressed as dry basis content, ≥90% is high purity) needs to be paid special attention to, and impurities (such as NaCl, Na₂CO₃, heavy metal ions) will interfere with the stability of the flotation system.
Impurity influence: Salts such as sodium chloride will increase the ionic strength of the ore pulp, which may destroy the hydration membrane structure of CMC and reduce the inhibition efficiency; heavy metal ions (such as Fe³⁺, Cu²⁺) will complex with the carboxyl group of CMC, causing CMC to fail or precipitate;
Selection principle: Complex polymetallic ores (such as copper, lead and zinc ores) or high-salt ore pulp (seawater flotation) require high-purity CMC (≥95%) to reduce the interference of impurity ions; simple ores or fresh water flotation can use industrial-grade purity (90%~95%) to balance cost and effect.
1.4 Solubility performance: ensure uniform inhibition
The dissolution rate and solution stability (no flocculation, no stratification) of CMC directly affect its dispersion uniformity in the ore pulp, and thus affect the stability of the inhibition effect.
Key influencing factors: Particle size: Fine powder (80 mesh pass rate ≥ 95%) dissolves faster than coarse particles and is suitable for flotation processes that require rapid onset; Degree of substitution and process: CMC with high DS and surface treatment (such as granulated products) dissolves more evenly and is not easy to agglomerate;
Selection principle: Continuous flotation processes (such as large-scale concentrators) require instant CMC to avoid excessive or insufficient local inhibition caused by incomplete dissolution; conventional soluble CMC can be used for intermittent flotation or low-dosage scenarios, but sufficient stirring time must be ensured (usually 15 to 30 minutes).
2. Adaptability selection combined with flotation process conditions.
2.1 Ore type and target mineral.
Sulfide ore flotation (such as copper, lead, zinc): silicate gangue such as quartz and feldspar needs to be suppressed, and medium-high DS (0.8~1.0) and medium viscosity (200~500 mPa·s) CMC are preferred to avoid excessive suppression of sulfide minerals (such as pyrite);
Oxide ore flotation (such as hematite, magnesite): The slurry is mostly alkaline (pH 8~11), and CMC is fully dissociated, requiring high DS (1.0~1.2) and high purity products to resist ion interference in a high alkaline environment;
Salt lake ore/high salt ore: The concentration of Ca²⁺ and Mg²⁺ in the slurry is high, and ultra-high purity (≥98%) and high DS CMC are required to reduce the complexation loss with metal ions.
2.2 Slurry environmental parameters
pH value: CMC dissociates more fully under alkaline conditions (pH>7), with high negative charge density and strong inhibitory effect; under acidic conditions (pH<5), dissociation is inhibited, and it is necessary to increase the dosage or select high DS products to compensate for the decrease in adsorption capacity;
Ionic strength: In high-salt slurry (such as containing a large amount of Na⁺, Ca²⁺), high DS and low viscosity CMC are preferred to resist the damage of ions to the hydration membrane through strong charge density;
Slurry concentration and fineness: High-concentration or finely ground slurry (-200 mesh accounts for >80%) requires low-viscosity, fast-dissolving CMC to avoid deterioration of slurry fluidity.
2.3 Compatibility with other agents.
Collector type: If anionic collectors (such as xanthate, fatty acid) are used, the amount of CMC and DS must be controlled to avoid the failure of the collector due to competitive adsorption of negative charges; if cationic collectors are used, CMC can form hydrogen bonds with it, and medium and low DS products must be selected to balance inhibition and collection;
Influence of adjusters: When lime (CaO) is added to the slurry, Ca²⁺ may complex with CMC, and the purity of CMC needs to be increased or the amount of CMC needs to be increased; when water glass is added, it can work with CMC to inhibit gangue, and the viscosity requirements of CMC can be reduced at this time.
3. Verification and optimization methods
3.1 Small-scale screening: Through single-factor tests (fixed dosage, variables are DS, viscosity, purity), the flotation concentrate grade, recovery rate and gangue content are tested to determine the preliminary index range;
3.2 Pilot verification: Simulate the flotation process in the actual slurry system to examine the dispersibility, inhibition stability and impact of CMC on subsequent operations (such as filtration);
3.3 Cost balance: High-index CMC (high DS, high purity) has better effects but higher costs, and it is necessary to select a cost-effective solution in combination with the ore value (such as precious metal ore vs. non-metallic ore).
Summary
The selection of indicators of sodium carboxymethyl cellulose in mining flotation should be centered on ore properties and guided by flotation goals. Priority should be given to substitution degree (regulating adsorption selectivity), viscosity (balancing inhibition strength and fluidity), purity (reducing interference) and solubility (ensuring uniformity), and comprehensive optimization should be carried out in combination with slurry environment, reagent compatibility and cost, and finally the optimal parameters should be determined through experimental verification.
