Grades

What it is for

Tracking the chemical assays of the streams (Fe, SiO2, Au…), calculating the grades you did not specify and the distribution of each analyte among the products (metallurgical recovery). It also lets you calculate the mass recovery of a separator from the grades.

Step by step

1. Set up the project analytes: Project ▾ → Grades… (or Project settings → Grades). For each analyte choose the unit: % (by weight), g/t or ppm.
   • Add ore package adds the typical set at once (iron ore, copper, gold, lateritic nickel, zinc and lead, lithium, phosphate, potash, bauxite, manganese, niobium, coal, rare earths, graphite). Analytes the project already has stay as they are.
   • The shortcuts in My analytes (your account lists) and Suggestions add with one click.
   • The star ☆ next to a project analyte saves it to or removes it from My analytes.
2. Enter the Feed grades in the Feed panel. Blank = not assayed.
3. Enter the grades measured at the separator outlets, in the analyte × outlet grid of the separator panel, or in the stream panel.
4. Read the results in the stream table and in Balance closure → Grades and distribution.

How grades are calculated

• Mixing: the grade is weighted by solids mass.
• Tanks, splitters, distributors, thickeners and filters: all outlets keep the grade of the mixture. They do not ask for grades.
• Separators: outlets with a specified grade keep it; the others share the remaining analyte in proportion to mass. With nothing specified, all outlets have the feed grade.
• A stream with solids and a not assayed analyte makes the grade unknown in every mixture it enters (shown as "—").

In the separator grid, what the balance calculated shows in grey; what you type shows in blue bold.

Mass recovery from grades

On two-outlet separators (magnetic separator without middlings, mass split and two-outlet concentration/classification units), the Mass recovery field in the panel has the option From … grades:

1. Choose the key analyte (for example, Fe).
2. Enter the grade of that analyte on both outlets.
3. The panel shows the Calculated recovery, from the classic two-product balance, using the feed grade and the grades of the two outlets.

If the feed grade does not fall between the two specified grades, the recovery is limited and the balance warns.

It does not apply with a middlings product (three products would need two analytes). To turn on middlings on a WHIMS, first set the recovery back to Specified.

Results

• Stream table: one "… grade" row per analyte, in the Grades group, which can be collapsed.
• Balance closure → Grades and distribution: grade and share of the analyte in each process Feed and Product. At the product of interest, this is the metallurgical recovery.

Impossible grades

In red bold, with the reason on hover (and written in the stream panel):

• grade in % above 100;
• grade set to zero because the grades specified on the other outlets require more analyte than comes in.

A grade above 100 % also appears on downstream streams, with the note "it comes from … grades specified upstream". With the Grades group collapsed, the Grades row shows in red how many impossible grades there are.

Typical cause: grades specified on the outlets of a classifier that do not close with the feed (for example, the underflow taking almost all the mass at a grade well below the feed grade).

Common warnings and limits

• Grade by size class does not exist yet. Units that separate by size (screen by aperture, cyclone) give the same grade on both outlets, unless you enter the measured grades.
• Grades specified on all outlets that do not close with the feed produce a warning.
• The program does not convert grade units (% to g/t, etc.).
• The PDF includes the grade rows of the stream table and, below the balance closure box, the "Grades and distribution" box.