How to transform the raw ore into tin ore concentrate?

Tin ore beneficiation is a complex process. Its core objective is to separate cassiterite (primarily composed of SnO₂) from gangue (unusual minerals) in the ore and enrich it into high-grade tin concentrate. Because cassiterite is dense and brittle, and often associated with various minerals, its beneficiation process typically relies primarily on gravity separation, supplemented by flotation, magnetic separation, and electrostatic separation.

1. Crushing and Screening

This is the preparatory stage for mineral processing, aiming to crush the raw ore to a suitable particle size for separation and then classify it through screening.

Coarse crushing: A jaw crusher is typically used to crush large ore (up to several hundred millimeters) to approximately 100-200 mm.

Secondary crushing: A cone crusher or impact crusher is typically used to further crush the coarse crushed product to 30-60 mm.

Fine crushing: A cone crusher or high-pressure roller mill is sometimes used for fine crushing in preparation for subsequent grinding.

Screening: Vibrating screens are a key piece of equipment in the entire crushing process. They control the particle size of the crushed product, screening out material of acceptable particle size while returning unacceptable coarse particles to the crusher for further crushing (forming a closed-circuit crushing process), improving efficiency and preventing over-crushing.

The goal of this stage is to obtain a material with a uniform particle size suitable for grinding.

2. Grinding and Classification

The purpose of grinding is to separate cassiterite from its associated minerals, that is, to separate the useful cassiterite particles from the composite ore.

Grinding: The core equipment is a ball mill or rod mill. Ball mills use steel balls as a grinding medium to impact and grind the ore; rod mills use steel rods, resulting in a more uniform product particle size and less over-crushing. They are often used for grinding before gravity separation.

Classification: Grinding is usually performed in a closed circuit with the classifier. A commonly used classifier is a hydrocyclone. It uses centrifugal force to classify the slurry by particle size. The overflow (fine particles) enters the next separation stage, while the sediment (coarse particles) returns to the mill for further grinding.

The key to this stage is to control the appropriate grinding fineness. Too coarse grinding will not separate the cassiterite, resulting in low recovery rates; too fine grinding will produce a large amount of sludge, which not only increases energy consumption but also seriously affects the subsequent gravity separation results. The basic principle is “more crushing, less grinding.”

3. Core Selection Stage

This is the core stage of cassiterite recovery, primarily focusing on gravity separation.

Roughing:

Equipment: Jigs are the preferred equipment for roughing coarse tin ore (above 2mm), offering high throughput and recovery rates. For finer tin ore, spiral chutes or shaking tables are often used.

Purpose: Rapidly obtain coarse concentrate and discard some qualified tailings.

Concentration:

Equipment: Shaking tables are the most critical and classic equipment for tin ore concentrating. They utilize the reciprocating motion of the bed bars and the action of water flow to precisely separate the ore, producing a variety of products including concentrate, middlings, and tailings. They handle a wide particle size range (0.037-2mm) and offer high separation accuracy.

Purpose: Multiple re-enrichment of the coarse concentrate to obtain high-grade tin concentrate.

Slime Treatment:

Conventional gravity separation equipment is inefficient for fine sludge below -0.037mm. Commonly used:

Centrifugal concentrators (such as belt chutes and Falcon centrifuges): Utilize centrifugal force to enhance fine-grained gravity separation.

Flotation: When cassiterite is extremely fine or closely associated with minerals such as sulfides, flotation is used. Special collectors (such as phosphonic acid and arsenic acid) are used to float the cassiterite. Sometimes, sulfides (such as pyrite and arsenopyrite) are also floated prior to gravity separation to eliminate their interference.

Purpose: Recovering fine cassiterite from fine mud is key to improving overall recovery, but also presents a challenge.