AU2007100072B4 - Method for Agglomeration - Google Patents

Description

AUSTRALIA

ORIGINAL

COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: Name of Applicant: Actual Inventor(s): Address for service: Method for Agglomeration Murrin Murrin Operations Pty Ltd Michael Rodriguez WRAY ASSOCIATES Level 4, The Quadrant 1 William Street Perth, WA 6000 Attorney code: WR The following statement is a full description of this invention, including the best method of performing it known to me:- -2- "Method for Aggqqlomeration" Field of the Invention The present invention relates to a method for agglomeration. More particularly, the present invention is intended to produce agglomerates of an ore to be leached using a relatively dilute acid solution in agglomeration.

Background Art Agglomeration is an ore treatment method that has been used extensively in the mining industry to improve the ore's leaching characteristics. Agglomeration typically involves the binding of finer particles, including clays, to larger particles.

This improves the percolation of leach solutions through the ore material and prevents migration of those finer particles. Additionally, this ensures that the target metal values contained in the fine materials are available to the leaching solution.

A variety of methods for agglomeration have been practised over the years, the simplest method involving the use of water to form the agglomerated particles.

Water is popular from an economic viewpoint, but its use is highly dependent on the ore characteristics. Ores with particularly high clay and/or fines content may not necessarily respond as well to water agglomeration.

For this reason binding agents became very popular, and the use of such agents has been adopted extensively. However, binding agents, such as cement, are generally only used in alkaline leaching conditions as many of these binding agents are not stable in low pH conditions.

Strong or concentrated acid has been a popular choice for agglomerating when binding agents are not suitable. In particular, the general trend is that the more concentrated the acid the more advantageous the results, although the use of concentrated acid is generally limited by economic factors. The advantages of concentrated acid are known to be that heat is generated by the exothermic reaction of the acid and the small amount of moisture present in the ore, resulting 3 in better break-down of the ore minerals and exposing the target metal values.

Concentrated acid also helps to form better agglomerates by breaking down bulk non-valuable minerals in the ore, for example silicates, particularly in laterites, such that upon re-precipitation and curing, a relatively strong agglomerate can be formed.

One of the main problems with using concentrated acid solutions in agglomeration is that agglomerates can become friable, resulting in blockages in the heap, once particles begin to break away. Further, the use of concentrated acid can also promote dissolution of unwanted impurities.

The present invention disclosed herein relates to the use of a dilute acid solution for agglomeration with surprising results. The disadvantages of using water or strong or concentrated acid appear to be overcome, without sacrificing structural integrity of the agglomerates, whilst percolation rates and extraction levels are improved.

The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Throughout the specification, the term "atmospheric" when used with reference to leaching is to be understood to refer to any one of a heap, vat, dump, thin-layer or in-situ leach, unless the context requires otherwise.

Throughout the specification, the terms "ore" and "ore material" are understood to refer to any one of ore, ore reject material, concentrate, waste rock or mill scats material.

The term "agglomerate" is to be understood to refer to agglomerated ore material.

Throughout the specification, the term "curing" is understood to be the period of time occurring between agglomeration and subsequent application of leaching solution.

Disclosure of the Invention In accordance with the present invention there is provided a method for agglomeration comprising the method steps of: i) adjusting the moisture content of an ore material to be agglomerated to a predetermined level; ii) passing the ore material to an agglomeration circuit; and iii) adding an acid containing agglomerating solution to the ore material in the agglomeration circuit to provide an agglomerated ore material, the acid concentration of the agglomerating solution not exceeding about Preferably, the acid in the agglomerating solution is any one of sulphuric, hydrochloric or nitric acid.

Preferably, the moisture content of the ore material prior to agglomeration falls within the range of about 5% and Still preferably, the moisture content of the ore material prior to agglomeration falls within the range of about 10% and The agglomeration circuit may comprise one ore more drum or rotary disc agglomerators.

The agglomerating solution of step iii) still preferably comprises a pregnant leach solution (PLS) from an existing atmospheric or pressure leach circuit.

Preferably, the agglomeration of step iii) is achieved by adding a maximum of about 50 kg of sulphuric acid per tonne of ore material.

Still preferably, the agglomeration of step iii) is achieved by adding a total amount of acid which falls within the range of about 5 and 50 kg of acid per tonne of ore.

Preferably, a binding agent is applied to the ore material in the agglomeration circuit.

Still preferably, the binding agent may comprise any known binding agent, for example sodium silicate.

Curing time of the agglomerates preferably does not exceed 7 days.

Preferably, curing time of the agglomerates falls within the range of about 5 and 7 days.

Brief Description of the Drawings The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawing, in which; Figure 1 is a diagrammatic representation of a method for agglomeration in accordance with the present invention.

Best Mode(s) for Carrying Out the Invention In Figure 1 there is shown a method for agglomeration 10 in accordance with the present invention.

6 An ore 12 is subjected to a preparation step 14 during which the moisture content is adjusted to within about 5% and 25%, for example 10% and 20%. This moisture content may be achieved by air drying the ore in a heap 16, or by adding water 18 to the ore, as required.

The ore 12 is then passed to an agglomeration circuit 20 where an acid containing agglomerating solution 22 containing between about 5 and 50g/L of sulphuric acid, and a known binding agent 24, is added, and the ore 12 agglomerated to provide an agglomerated ore material 26.

The agglomerated ore material 26 is then cured for a period of time. The curing time should not exceed 7 days as the stability of the agglomerated ore material 26 begins to deteriorate after this time. The balance between the stability of the agglomerated ore material 26 and permeability and extraction is maximised when the curing time falls within the range of 5 and 7 days.

The agglomeration circuit 20 may comprise one ore more drum or rotary disc agglomerators.

It is envisaged that the acid containing agglomerating solution 22 may comprise a dilute sulphuric acid solution, or a leach solution exiting an atmospheric or pressure leach circuit, or a mixture of both, such that the acid concentration falls within the range of about 5 to 50 kg acid per tonne of ore.

It is further envisaged that the acid in the agglomerating solution may alternately comprise any one of nitric and hydrochloric acid.

The present invention is further illustrated by way of the following non-limiting example: EXAMPLE 1 Percolation testing, using a standard Kappes test procedure, was employed to measure the quality of the agglomerates produced using the method of agglomeration of the present invention. The Kappes percolation test involves filling a leaching column (0.1mm diameter and 0.6m height) with agglomerates and measuring the initial ore height.

The column is then filled from the bottom with leaching solution containing sulphuric acid such that the solution covers all of the ore. The column then stands for 48 hours and before the height of the agglomerates is measured again.

The column is tapped with a rubber mallet over its length so that the agglomerates are settled. The new height is then measured in order to determine the "slump" of the ore.

The percolation rate is then measured by opening the bottom drain valve, drained for an initial period of 5 seconds, then taking a timed sample of solution, measuring the quantity of solution discharged and calculating a flow rate in L/h rim 2 In order for the test to pass, a flow rate of at least 10,000 L/hr/m 2 and a slump of less than 10% must be achieved.

The Kappes percolation test results of various nickel laterite ore materials agglomerated with either leach solution from the pressure acid leach (HPAL) circuit, dilute acid solutions or concentrated acid are shown in Table 1. The term "Scats" is used to refer to the coarse fraction of the ore resulting from beneficiation.

Table 1 Ore Agglomeration Moisture Slump Percolation Material Solution Rate (Lhrlm 2 Low-grade HPAL leach 9.5 8.6 15144 Saprolitic Ore Strong acid 9.5 14.9 351 (150kg/t) Scats 41 Dilute acid (50 9.5 7.8 18694 kg/t) Strong acid (100 9.5 12.5 2292 kg/t) Dilute acid (50 7.9 7.1 13487 kg/t) Strong acid (100 7.9 9.6 306 kg/t) Scats #2 Dilute acid (50 25.4 15.3 28644 (effect of kg/t) moisture) Dilute acid (50 11.7 9.9 35254 kg/t) Dilute acid (50 6.5 8.9 21824 kg/t) Agglomerates produced with both 100 kg/t and 150 kg/t sulphuric acid had a tendency to break down during the flooding stage, resulting in a layer of fines a the top of the agglomerated material, which in tum, affected percolation.

As can been seen from the results in Table 1, agglomerating with dilute acid in comparison to strong acid resulted in the samples passing the Kappes test.

Further, the initial moisture content of the samples clearly alters the characteristics of the final agglomerates, affecting the percolation rates.

The ability to produce better agglomerates by controlling the moisture content of the ore material and the concentration of acid during agglomeration is shown to result in more stable agglomerates and better rates of percolation of leaching solution through the ore material. In turn, improved percolation rates lead to faster leaching kinetics and higher extractions.

Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention

Claims (5)

1. A method for agglomeration comprising the method steps of: i) adjusting the moisture content of an ore material to be agglomerated to a predetermined level, ii) passing the ore material to an agglomeration circuit; and iii) adding an acid containing agglomerating solution to the ore material in the agglomeration circuit to provide an agglomerated ore material, whereby the acid concentration of the agglomerating solution does not exceed about

2. A method according to claim 1, wherein the moisture content of the ore material prior to agglomeration falls within the range of about 5% and

3. A method according to claim 1 or 2, wherein the agglomerating solution of step (iii) comprises a pregnant leach solution (PLS) from an existing atmospheric or pressure leach circuit.

4. A method according to claims 1 to 3, wherein the agglomeration of step (iii) is achieved by adding up to about 50 kg of sulphuric acid per tonne of ore material.

5. A method according to any one of the preceding claims, wherein the curing time of the agglomerates does not exceed 7 days.