Grinding Circuit Circulating Load (Two-Product Formula)
How much a cyclone or screen sends back to the mill, from one size-class assay of the classifier feed, overflow.
Example
You enter
- Classifier feed, % in the size class (e.g. % passing 75 microns) 40
- Overflow, % in the same size class 70
- Underflow, % in the same size class 25
- New feed to the circuit (short tons per hour, blank for the ratio only) 100
You get
- Circulating load (%) 200
- Classifier feed stph 300
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeHow much a cyclone or screen sends back to the mill, from one size-class assay of the classifier feed, overflow, and underflow: U/O = (o - f)/(f - u). With 40% passing 75 microns in the feed, 70% in the overflow, and 25% in the underflow, the circulating load is 200%, so 100 st/h of new feed means 200 st/h back to the mill and 300 st/h to the cyclones. Ball mills usually run 150-350%. Steady state, dry solids. A screen; a full mass balance governs.
Formula or tableU/O = (o - f)/(f - u) on one size class (f classifier feed, o overflow, u underflow, percent); circulating load % = 100 U/O; underflow = (U/O) x new feed; classifier feed = new feed + underflow.
Source and editionThe two-product formula for a classifier closing a grinding circuit, a steady-state mass balance on one size class (as in Wills' Mineral Processing Technology), by name.
Free accessA mass balance on the user's own size assays; no published data is bundled.
What governsEstimate. AHJ and licensed professional govern.
API field namesfeed_pct, overflow_pct, underflow_pct, new_feed_stph, circulating_load_pct, classifier_feed_stph
- Two-product formula U/O = (o - f)/(f - u)mass balance; Wills
- Steady state overflow = new feed; no accumulation in the mill or sumpscope of this tile