Hydrometallurgy

Hydromet Slurry Calculations

The application hub for hydromet and slurry calculations — how slurry density, percent solids, flow, residence time, and reagent make-up/dosing connect across leach/CIL residence time, CCD wash water, thickener underflow density, reagent consumption, cyanide and lime make-up, and flocculant make-down, and where each ProcessConvert calculator fits. A concept and navigation guide, not a design model.

TypeEngineering guide — concept explainer

Definition

Hydromet slurry calculations are the set of preliminary engineering calculations that describe a mineral-processing slurry as it moves through a hydrometallurgical circuit: how much solid it carries, how dense it is, how fast it flows, and how long it spends in each unit. They share a common backbone — slurry density and percent solids fix the relationship between the dry solids mass flow and the slurry volumetric flow, and that volumetric flow then drives leach and CIL residence time, CCD wash-water requirements, and thickener underflow density. This guide is the hub that connects those tools; each one is a preliminary estimate, not a design model.

Why it matters

In a hydromet plant the same slurry is described in different ways at different points — t/h of dry solids at the mill, m³/h of slurry into the leach tanks, wt% solids in a thickener underflow, a wash ratio across a CCD train. If those descriptions are not kept consistent, the numbers downstream go wrong: a residence time computed on liquor flow instead of slurry flow is too long, a wash ratio computed without the right underflow density is meaningless, and a thickener underflow density quoted without its solids density is ambiguous. Working the calculations together — density and percent solids first, then flow, then residence time and wash water — keeps the basis consistent. It also keeps the right caveats attached: hydraulic residence time is not recovery, wash ratio is not soluble recovery, and underflow density is not thickener sizing.

Formula

Slurry density (mass basis)

ρ_slurry = 1 / (Xs/ρ_solids + (1−Xs)/ρ_liquid)

Slurry volumetric flow

Q_slurry = ṁ_slurry / ρ_slurry

Residence time

τ = V_online / Q_slurry

CCD wash ratio

wash ratio = Q_wash / Q_underflow liquor

Units involved

•ṁ_solids — dry solids mass flow in t/h
•ρ_slurry, ρ_solids, ρ_liquid — densities in kg/m³
•Xs — solids mass fraction (or wt% solids)
•Q_slurry — slurry volumetric flow in m³/h or L/s
•V_working — tank working volume in m³; τ in h
•Keep the same time basis (per hour) across mass and volume flows

Concept diagram

Worked example

A leach circuit treats 100 t/h dry solids at 55 wt% solids. Estimate the slurry flow, then the residence time across a 1800 m³ online tank train.

01Slurry mass: 100 / (55/100) = 181.82 t/h
02With a liquor density of 1000 kg/m³ the liquor is 81.82 t/h = 81.82 m³/h
03Add the solids volume (depends on solids density) to get the slurry volumetric flow
04Residence time: τ = V_online / Q_slurry — use the slurry flow, not the liquor flow
05Read τ against the leach kinetics; confirm wash water and underflow density separately

Result

The dry solids rate and wt% solids set the slurry mass and volumetric flow, which then drives residence time, CCD wash water, and thickener underflow density — each a preliminary estimate read together, not a single design answer.

Common mistakes

•Mixing a liquor (solution) flow with a slurry flow when computing residence time.
•Quoting a thickener underflow density without stating the solids density it assumes.
•Treating a CCD wash ratio as a soluble-recovery number.
•Reading leach residence time as a recovery guarantee independent of kinetics.
•Switching time bases (per second vs per hour) midway through a chain of calculations.

When to use the calculator

Start with the slurry density and percent-solids calculators to fix the basis, the slurry mass balance and blending calculators to move between mass and volume flows, then the leach/CIL residence-time, CCD wash-water, and thickener underflow density calculators for the application numbers. Every one is preliminary — the circuit design comes from testwork and process modelling.

FAQ

Which calculation should I do first?

Fix the slurry density and percent solids first — they tie the dry solids mass flow to the slurry volumetric flow. Once the volumetric flow is consistent, residence time, CCD wash water, and thickener underflow density all follow from it.

Why do these calculators keep warning that they are not design models?

Because each one answers a hydraulic or mass-balance question only. Recovery, stage efficiency, settling, and thickener performance depend on chemistry and testwork that a preliminary calculation cannot capture. The numbers scope the equipment; testwork and modelling design it.

Can I use slurry density from one stage everywhere?

No. Slurry density and percent solids change through the circuit — mill discharge, leach feed, thickener underflow, and tailings are all different. Use the density and percent solids that apply at the point you are calculating.

How does this hub relate to the individual guides?

This guide connects the pieces. The slurry density, percent solids, leach residence time, CCD wash ratio, and thickener underflow density guides go deeper on each topic; this one shows how they fit together and which calculator to reach for.