Unit
- Mineral processing chain: The sequence from mining to concentrate involves comminution, sizing, concentration, and dewatering. Each stage aims to liberate valuable minerals from gangue and upgrade the ore grade before downstream extraction.
- Liberation and recovery: Liberation is achieved by breaking ore particles to expose mineral surfaces. Recovery measures the fraction of valuable mineral captured in the concentrate. Both depend on particle size distribution and the mineralogical texture of the ore.
- Grade and recovery tradeoff: Increasing concentrate grade often reduces recovery because some valuable minerals are lost to tailings. Process design balances these metrics based on economic factors and downstream smelter requirements.
- Sampling and assaying: Representative sampling and chemical analysis (fire assay, XRF, ICP) are critical to quantify head grade, concentrate grade, and tailings losses. Statistical methods ensure sample representativity.
- Process flow sheets: A typical flow sheet includes primary crushing, SAG milling, ball milling, classification by hydrocyclones, flotation or gravity concentration, and thickening/filtration. Each unit operation is designed based on ore characteristics.
- Energy consumption: Comminution consumes up to 50% of the total energy in a mineral processing plant. Energy efficiency improvements through high-pressure grinding rolls (HPGR) and stirred mills are increasingly adopted.
- Water management: Water is used for transport, classification, and separation. Closed-loop water circuits and dry tailings disposal reduce environmental footprint and comply with regulations.
- Automation and control: Modern plants use distributed control systems (DCS) to monitor particle size, slurry density, and reagent addition. Advanced process control (APC) optimizes throughput and recovery.
- Crushing stages: Primary, secondary, and tertiary crushing reduce ore size from run-of-mine to a manageable feed for grinding. Jaw and gyratory crushers are common for primary, while cone crushers are used for secondary and tertiary stages. Reduction ratios and closed-side settings are optimized for throughput and downstream grinding efficiency.
- Grinding media: Steel balls or rods are used in tumbling mills to break ore particles by impact and abrasion. Ball charge volume, media size distribution, and mill speed influence grinding efficiency and wear. Ceramic or pebble media may be used to avoid iron contamination in downstream processes.
- Flotation reagents: Collectors, frothers, and modifiers selectively enhance hydrophobicity of target minerals and stabilize froth for separation. Reagent dosage and conditioning time are critical parameters, often determined through bench-scale tests and optimized via plant trials to maximize grade and recovery.
Code Example
Python
def mass_balance(feed_rate, feed_grade, conc_grade, tail_grade):
# Solve for concentrate and tailings flows
conc_rate = feed_rate * (feed_grade - tail_grade) / (conc_grade - tail_grade)
tail_rate = feed_rate - conc_rate
recovery = (conc_rate * conc_grade) / (feed_rate * feed_grade) * 100
return conc_rate, tail_rate, recovery
# Example: feed 100 t/h at 1.2% Cu, concentrate 28% Cu, tailings 0.15% Cu
c, t, r = mass_balance(100, 1.2, 28, 0.15)
print('Concentrate: {:.2f} t/h'.format(c))
print('Tailings: {:.2f} t/h'.format(t))
print('Recovery: {:.2f}%'.format(r))This Python function solves a two-product mass balance. It calculates concentrate and tailings flow rates and the recovery percentage. The example uses copper ore data to illustrate typical metallurgical accounting.
Quick Revision
- Mineral processing consists of comminution, sizing, concentration, and dewatering stages.
- Liberation of valuable minerals from gangue is essential for effective separation.
- Grade and recovery exhibit an inverse relationship; design decisions consider economic value.
- Sampling and assaying provide data for process control and reconciliation.