24-MMP-B5 Mineral Processing Design and Operations · May 2016
Question 7 of 8: Gold flotation-roast-cyanidation flowsheet sizing
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exam 09-MMP-B5, Mill Design & Operations — May 2016, 3 hours. Candidates were instructed to answer any 6 of the 8 questions (each of equal value); all 8 are solved below as a complete study resource.
Reference texts: Wills' Mineral Processing Technology (B.A. Wills & J. Finch, 8th ed., Butterworth-Heinemann) — Ch. 4 Comminution, Ch. 8 Screening, Ch. 9 Classification, Ch. 12 Froth Flotation, Ch. 14 Solid-Liquid Separation; Mular, Halbe & Barratt (eds.), Mineral Processing Plant Design, Practice and Control (SME, 2002); Mular & Poulin, CIM Special Volume 47 (1998) preliminary capital cost estimation; SME Mining Engineering Handbook (3rd ed.).
Given. Plant feed 20,000 t/day, ore SG 3.1, calcine SG 2.93. Rougher feed = plant feed × (1 + 25% scavenger circulating load); rougher slurry 40% solids by wt.; rougher retention 12 min; cell size 50 m³, 20% dead volume. Calcine (cyanidation feed) = 22.5% of plant feed by wt. = 4,500 t/day; cyanidation slurry 50% solids by wt.; retention 35 h; tank size 750 m³, 22% dead volume.
Find. (a) Number of rougher flotation cells. (b) Number of cyanidation tanks.
Fig. 4 — Simplified gold flowsheet: sulphide ore to roughers/scavengers (25% scavenger circulating load back to roughers), bulk concentrate to fluidized-bed roasting, calcine to cyanidation, then activated-carbon recovery.
Approach. For each vessel, compute the slurry volumetric flow rate from the solids tonnage, SG and % solids, multiply by the stated retention time for the required active (working) volume, then divide by each vessel's own usable (post-dead-space) volume and round up.
Rougher feed and slurry volume. Rougher feed tonnage includes the scavenger circulating load:
$$\dot m_{\text{rougher}}=20{,}000\times(1+0.25)=25{,}000\ \text{t/day (solids)}$$
At 40% solids by weight (SG$_\text{ore}$ = 3.1, water SG = 1.0), solids and water volumes:
$$V_{\text{solids}}=\frac{25{,}000}{3.1}=8{,}064.5\ \text{m}^3/\text{day} \qquad V_{\text{water}}=25{,}000\left(\frac{1}{0.40}-1\right)=37{,}500\ \text{m}^3/\text{day}$$
$$V_{\text{slurry}}=8{,}064.5+37{,}500=45{,}564.5\ \text{m}^3/\text{day}=31.64\ \text{m}^3/\text{min}$$
Required active rougher volume and cell count.
$$V_{\text{active}}=31.64\ \text{m}^3/\text{min}\times12\ \text{min}=379.7\ \text{m}^3$$
Usable volume per 50 m³ cell (20% occupied by agitator/aeration): $50\times0.80=40\ \text{m}^3$.
$$n_{\text{cells}}=\left\lceil\frac{379.7}{40}\right\rceil=\boxed{10\ \text{cells}}$$
Cyanidation feed and slurry volume. Calcine feed $=20{,}000\times0.225=4{,}500\ \text{t/day}$ (consistent with 30% flotation recovery less 25% roasting mass loss: $20{,}000\times0.30\times(1-0.25)=4{,}500\ \text{t/day}$). At 50% solids by weight (SG$_\text{calcine}$ = 2.93):
$$V_{\text{solids}}=\frac{4{,}500}{2.93}=1{,}536.5\ \text{m}^3/\text{day} \qquad V_{\text{water}}=4{,}500\left(\frac{1}{0.50}-1\right)=4{,}500\ \text{m}^3/\text{day}$$
$$V_{\text{slurry}}=1{,}536.5+4{,}500=6{,}036.5\ \text{m}^3/\text{day}$$
Required active cyanidation volume and tank count.
$$V_{\text{active}}=6{,}036.5\ \text{m}^3/\text{day}\times\frac{35\ \text{h}}{24\ \text{h/day}}=8{,}803.5\ \text{m}^3$$
Usable volume per 750 m³ tank (22% occupied): $750\times0.78=585\ \text{m}^3$.
$$n_{\text{tanks}}=\left\lceil\frac{8{,}803.5}{585}\right\rceil=\boxed{16\ \text{tanks}}$$
