Feldspar ore (potassium-bearing pegmatite or albite-rich rock) is extracted by open-pit quarrying. ROM ore (200–800 mm lumps) is transported to the primary crushing station. In dry processing, all subsequent stages are conducted without water addition — the ore must be naturally dry or must be pre-dried before processing begins. Selective mining of high-purity ore zones is the first quality control step in dry processing — since dry beneficiation methods are less effective at fine-grained iron removal than wet methods, the quality of the starting ore determines the quality ceiling of the dry-processed product.

ROM ore is fed into a jaw crusher (400×600 mm to 900×1200 mm jaw opening) which reduces 200–800 mm lumps to 20–50 mm product. The jaw's compressive action breaks ore along natural grain boundaries and cleavage planes where possible. In dry processing, the crushed product is immediately screened and conveyed without water — dust suppression must be managed carefully at this stage, as silica dust from feldspar is a serious occupational health hazard (respirable crystalline silica). Proper water-spray dust suppression at the crusher — without introducing enough water to affect the process — is standard practice in responsible dry operations.

Primary crushed material (20–50 mm) is reduced to 5–15 mm by a cone crusher or impact/hammer mill. Cone crushers produce more cubical particles (better for coarse aggregate applications); hammer mills produce more angular particles and more fines. Screening at this stage separates the material into size fractions and removes excess fines. The 5–15 mm crushed ore is the feed material for the most important dry beneficiation step — high-intensity dry magnetic separation.

If the crushed ore contains more than 1–2% surface moisture (from rainfall, seasonal humidity, or the ore deposit itself), it must be dried before dry magnetic separation and grinding. Rotary drum dryers (direct-fired, natural gas preferred for white feldspar) dry the material to <0.5% moisture at 150–250°C inlet temperature. Dry magnetic separators lose effectiveness when feed material is moist — wet particles clump and bridge, reducing iron mineral liberation and separation efficiency. For operations in high-humidity climates (tropical Asia, monsoon India), this drying step is particularly important.

This is the primary and most critical iron-removal step in dry feldspar processing. Dried, crushed feldspar (5–15 mm) is fed over a high-intensity dry magnetic separator (HIDS) — typically an induced roll magnetic separator or rare-earth roll separator operating at 0.8–1.8 Tesla field strength. Iron-bearing minerals (biotite, hornblende, magnetite, hematite, ilmenite) — all paramagnetic or ferromagnetic — are attracted to the magnetic roll and deflected into a separate collection bin. Clean, diamagnetic feldspar passes through the non-magnetic product chute. Multiple passes (2–3 stages of magnetic separation) are typically used to progressively reduce iron content. The limitation of dry magnetic separation: it is less effective for very finely disseminated iron — iron oxide films on grain surfaces, iron within clay mineral intergrowths, and ultra-fine hematite coatings are not fully removed by dry methods alone. This is the fundamental quality ceiling of dry-processed feldspar compared to wet-processed material.

Dry-magnetically-separated, pre-dried feldspar (5–15 mm) is fed to the grinding mill: Steel ball mill (most common for large-scale production; 1.5–4.5m diameter; open or closed circuit) or Raymond mill / vertical roller mill (for precision cuts at 200–325 mesh; built-in air classification; better energy efficiency). In dry ball milling: grinding media (forged steel balls, 20–80mm diameter) impart repeated compressive and shear impacts that fracture feldspar particles. The key dry grinding characteristic: particles fracture preferentially along cleavage planes and grain boundaries — since there is no water lubricant to direct fracture energy, particles break more randomly, producing a broader particle size distribution (PSD) compared to wet grinding. This broader PSD is a defining characteristic of dry-ground feldspar and has both advantages (some coarse particles for certain applications) and disadvantages (more ultrafines, less sharp PSD cutoff) compared to wet-ground material.

Ground feldspar exits the mill and enters a dynamic air classifier — a machine that uses centrifugal force and aerodynamic drag to separate fine on-specification particles from coarse rejects. The air classifier's rotor speed controls the cut point. For a 200-mesh (75µm) specification, the classifier is adjusted to pass ≥95% of particles below 75µm. Coarse rejects return to the mill for regrinding (closed-circuit grinding). Fine product is collected by bag filters downstream. A key limitation of air classification vs. wet screening: it is less precise, with a broader separation efficiency curve (Tromp curve). This means dry classified products typically have a less sharp PSD (more oversize tailing, more ultrafine fraction) compared to wet-sieved or wet-classified equivalents. The classifier's performance also degrades with temperature changes, humidity fluctuations, and mechanical wear — requiring regular calibration.

Dry-processed feldspar is sampled after classification and tested for: chemical composition (XRF — full oxide analysis), particle size (sieve analysis and/or laser diffraction), whiteness/brightness (ISO 2470), moisture (LOI at 105°C), and bulk density. Approved product is packaged in moisture-proof PE-lined bags (25 kg, 50 kg) or FIBC jumbo bags (500–1000 kg) and stored in covered warehouses. Dry feldspar is hygroscopic — it absorbs atmospheric moisture and can cake if packaging is not moisture-proof or if storage conditions are humid. Proper packaging is critical for maintaining the product's free-flowing character and specified moisture content (<0.5%).

The upstream mining, primary jaw crushing, and secondary cone/impact crushing stages are identical to dry processing. Crushed feldspar at 5–15 mm is the feed material for wet beneficiation. The key decision point is at the transition from coarse crushing to beneficiation — in wet processing, water is introduced at this stage and the material travels the remainder of the processing route as a slurry. The crushed ore does not need to be pre-dried before wet processing — in fact, wet processing is better suited to ores that are naturally moist or located in humid climates.

Crushed feldspar is slurried with water (30–35% solids by weight) in attrition scrubbing cells — high-shear mixing vessels where particle-on-particle friction removes: clay coatings from grain surfaces, iron oxide (hematite, goethite) films on mineral surfaces, fine silt and clay mineral intergrowths, and weakly bonded organic matter. The attrition scrubbing step alone can reduce Fe₂O₃ by 20–40% of the initial iron content. This is a critical distinction from dry processing — dry magnetic separation targets liberated iron-bearing minerals, while wet attrition scrubbing removes surface iron coatings that dry methods cannot access. The resulting slurry is deslimed in hydrocyclones to remove the fine clay and iron-bearing fraction (<10–20µm) that carries the liberated impurities.

The deslimed feldspar slurry is fed through a wet high-gradient magnetic separator (WHGMS) — the most powerful and effective iron-removal technology available for industrial minerals. The WHGMS uses a matrix of fine stainless steel wool or grooved steel plates within a high magnetic field (0.5–1.8 Tesla) to trap weakly magnetic iron minerals from the flowing slurry. Because the feldspar is in slurry form: individual mineral particles are fully dispersed (no agglomeration as in dry separation), contact between iron minerals and the magnetic matrix is maximised, very fine iron particles (<50µm) that escape dry HIDS are captured, and iron oxide films loosened by attrition scrubbing are removed from the slurry stream before they can re-adhere. The WHGMS achieves Fe₂O₃ levels of 0.03–0.08% — significantly better than dry processing — in the best operations. This is the technology that makes ultra-white feldspar powder possible.