Mineral separation and recovery method for silver and manganese in silver manganese ore

Abstract

The invention provides a beneficiation separation and recovery method for silver and manganese in silver manganese ore, which comprises the following steps of: crushing raw silver manganese ore to obtain a crushed product; the crushed product is pretreated through dry magnetic separation, and a magnetic product containing silver and manganese and a non-magnetic product containing silver are obtained; the non-magnetic products are subjected to flotation to recover silver, and silver concentrate 1 and silver tailings 1 are obtained; the magnetic product is subjected to flotation to recover silver, and silver concentrate 2 and silver tailings 2 are obtained; and the silver tailings 2 are subjected to flotation to recover manganese, and manganese concentrate and manganese tailings are obtained. Dry magnetic separation is adopted for pretreatment, the flotation selection grade of silver and manganese is improved, mutual interference of follow-up silver and manganese separation and recovery is reduced, high-grade silver concentrate and manganese concentrate can be obtained easily, the comprehensive utilization level of ore resources is improved, and meanwhile the economic benefits of mine enterprises can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of mineral processing, in particular to a mineral processing, separation and recovery method for silver and manganese in silver-manganese ore. Background Art

[0002] Silver-manganese associated deposits refer to silver-manganese associated deposits with a silver grade of not less than 40g / t. They are an important type of silver resource. Currently, the manganese content in the silver-manganese ores that have been discovered in China exceeds 5.0×10 7 t, the amount of silver metal is nearly 1.0×10 4 Silver-manganese ore's associated silver minerals primarily occur in the form of native silver, gold-silver ore, and silver-gold ore. These occur as fine particles, isomorphically embedded within the manganese ore lattice. This makes it difficult to obtain high-grade silver concentrate through mechanical separation, and difficult to achieve good silver leaching performance through a single cyanidation process. This makes it widely recognized as one of the most difficult silver-bearing ores to treat. To date, there is still no mature and adaptable silver-manganese ore treatment process, and different treatment processes are selected based on the specific properties of the ore.

[0003] Silver and manganese in silver-manganese ore have a very close relationship, and silver-manganese separation is the key to the comprehensive recovery of silver-manganese ore. Common manganese-silver separation processes include gravity separation, magnetic separation, flotation, high-temperature reduction roasting acid leaching of manganese, low-temperature reduction leaching, etc., which can be roughly divided into physical separation and chemical separation. In general, for complex silver-manganese ores, single gravity separation, magnetic separation or flotation methods are difficult to effectively separate manganese minerals and silver minerals, although the combined process (ore concentration-wet leaching) can improve the recovery rate. However, the process is complex, the technology is not mature, and the production cost is high, making it difficult to apply it in large-scale industry.

[0004] A silver-bearing rhodochrosite ore, primarily composed of rhodochrosite (siderite), argentite, pyrite, quartz, and dolomite, contains approximately 300-600 g / t of silver and 5-15% manganese. The silver minerals are primarily embedded in iron-manganese carbonate minerals and quartz as fine-grained disseminated minerals. Conventional recovery processes, such as flotation silver-magnetic separation for manganese or flotation silver-manganese separation for flotation silver-flotation, yield low silver recovery rates and low manganese grade and recovery rates, hindering effective comprehensive recovery. Treatments such as ultrafine grinding-leaching and ultrafine grinding-flotation-leaching are also costly. Furthermore, the low hardness of useful minerals such as rhodochrosite and argentite in the ore makes them prone to muddling during fine grinding, compromising the flotation environment and further complicating the separation and recovery of silver and manganese. Therefore, a beneficiation method with low production and operating costs and high silver and manganese separation and recovery efficiency is urgently needed for this type of silver-manganese ore. Summary of the Invention

[0005] The present invention provides a method for separating and recovering silver and manganese in silver-manganese ore, which adopts dry magnetic separation for pretreatment, thereby improving the flotation selection grade of silver and manganese, and is conducive to obtaining high-grade silver concentrate and manganese concentrate.

[0006] The technical solution of the present invention is achieved as follows: a method for separating and recovering silver and manganese from silver-manganese ore, comprising the following steps:

[0007] (1) crushing the silver-manganese ore to obtain a crushed product;

[0008] (2) pre-treating the crushed product by dry magnetic separation to obtain a magnetic product containing silver and manganese and a non-magnetic product containing silver;

[0009] (3) flotation-recovering silver from the non-magnetic product to obtain silver concentrate 1 and silver tailings 1;

[0010] (4) flotation-recovering silver from the magnetic product to obtain silver concentrate 2 and silver tailings 2;

[0011] (5) flotation is performed on the silver tailings 2 to recover manganese to obtain manganese concentrate and manganese tailings.

[0012] Furthermore, in step (3) and step (4), the non-magnetic product and the magnetic product need to be ground before flotation to recover silver, and the grinding fineness is -0.074mm, accounting for 70%-90%.

[0013] Furthermore, in step (1), the upper limit of the crushing particle size is 5-8 mm.

[0014] Furthermore, in step (2), the magnetic field strength of the dry magnetic separation is 500-800 kA / m.

[0015] Furthermore, in step (3) and step (4), the flotation recovery of silver includes a roughing stage, 2-3 cleaning stages and 2-3 scavenging stages, wherein the roughing stage obtains a silver concentrate, and the silver concentrate is subjected to 2-3 cleaning stages to obtain silver concentrate 1 or silver concentrate 2.

[0016] Furthermore, in step (5), flotation recovery of manganese includes a roughing stage, 2-3 cleaning stages and 2-3 scavenging stages, wherein the roughing stage obtains a manganese concentrate, and the manganese concentrate is subjected to 2-3 cleaning stages to obtain a manganese concentrate.

[0017] Furthermore, in step (3) and step (4), the silver recovered by flotation is flotated by adding an inhibitor, an activator, a collector and a frother, wherein the inhibitor is water glass, sodium hexametaphosphate or carboxymethyl cellulose, the activator is copper sulfate or lead nitrate, the collector is one or more of butyl xanthate, amyl xanthate and butyl ammonium black medicine, and the frother is pine oil or methyl isobutyl carbinol.

[0018] Furthermore, in the rough selection of step (3) and step (4), the inhibitor is 500g / t-2000g / t of water glass, 50g / t-200g / t of sodium hexametaphosphate or 200g / t-800g / t of carboxymethyl cellulose; the amount of activator is 50g / t-200g / t, the amount of collector is 50g / t-200g / t, and the amount of foaming agent is 10g / t-30g / t.

[0019] Furthermore, in step (5), manganese is recovered by flotation by adding a pH adjuster, an inhibitor, an activator and a collector for manganese flotation, wherein the pH adjuster is one or more of sodium carbonate, sodium hydroxide and lime, the inhibitor is water glass, sodium hexametaphosphate or carboxymethyl cellulose, the activator is aluminum sulfate, and the collector is one or more of oleic acid, oxidized paraffin soap or sodium petroleum sulfonate.

[0020] Furthermore, in the rough selection in step (5), the amount of pH adjuster is 500g / t-2000g / t, the amount of inhibitor is 100g / t-2000g / t, the amount of activator is 100g / t-300g / t, and the amount of collector is 200g / t-500g / t.

[0021] Furthermore, in step (2), the dry magnetic separation includes two stages of magnetic separation, namely, roughing magnetic separation and scavenging magnetic separation. The magnetic field strength of the roughing magnetic separation is 500-600 kA / m, and the magnetic field strength of the scavenging magnetic separation is 700-800 kA / m.

[0022] Furthermore, in step (1), the mineral composition of the silver-manganese ore mainly includes rhodochrosite, argentite, pyrite, quartz and dolomite, etc., containing 300-600 g / t of Ag and 5 wt.%-15 wt.% of manganese. The silver minerals are mainly embedded in the iron-manganese carbonate minerals and quartz minerals in the form of fine particles.

[0023] Beneficial effects of the present invention:

[0024] The present invention provides a method for beneficiation, separation and recovery of silver and manganese in silver-manganese ore. Dry magnetic pre-selection is adopted to separate the ore into a non-magnetic product containing no manganese and a magnetic product containing manganese and silver before flotation recovery of silver and manganese. This method improves the selection grades of silver and manganese respectively, reduces the mutual interference in subsequent flotation separation and recovery of fine-grained silver and manganese, is conducive to obtaining high-grade silver and manganese concentrates, realizes the fine separation of silver and manganese, and further improves the comprehensive utilization rate of ore resources and the economic benefits of mining enterprises.

[0025] Moreover, the separation process of the present invention is all physical methods, without using metallurgical means, which greatly reduces production costs and improves mineral processing efficiency. In addition, the present invention uses dry magnetic separation equipment for magnetic separation, eliminating the desludging step required by wet magnetic separation equipment, making the mineral processing process simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 The present invention is a process flow chart of the silver-manganese beneficiation, separation and recovery method. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0029] Example 1

[0030] A silver-manganese ore contains Ag 509g / t and Mn 7.25%. The main mineral components are argentite, sideromanganese ore, quartz and dolomite.

[0031] (1) Use jaw crusher and cone crusher to crush the raw ore to less than 8mm;

[0032] (2) The crushed product is fed into a dry magnetic separation device for magnetic separation pretreatment. Through two stages of magnetic separation, namely roughing separation and sweeping separation, a magnetic product containing silver and manganese and a non-magnetic product containing silver are obtained respectively. The magnetic field strength of the first stage is 500 kA / m, and the magnetic field strength of the second stage is 750 kA / m.

[0033] (3) Non-magnetic products and magnetic products are ground separately. Specifically, the grinding fineness of non-magnetic minerals is -0.074mm, accounting for 70%, and the grinding fineness of magnetic materials is -0.074mm, accounting for 85%;

[0034] After grinding, the non-magnetic material was subjected to silver flotation by adding a depressant, activator, collector, and frother. The flotation process consisted of one roughing, two finishing, and two scavenging steps, yielding silver concentrate 1 and silver tailing 1. The depressant was water glass, the activator was copper sulfate, the collector was butyl xanthate, and the frother was pine oil. The roughing step used 500g / t of water glass, 50g / t of copper sulfate, 50g / t of butyl xanthate, and 10g / t of pine oil.

[0035] (4) The magnetic material after grinding treatment is subjected to silver flotation by adding an inhibitor, an activator, a collector and a frother. The flotation process is one roughing, two fines and two sweeps to obtain silver concentrate 2 and silver tailings 2. The inhibitor is sodium hexametaphosphate, the activator is copper sulfate, the collector is butyl xanthate, and the frother is pine oil. The amount of sodium hexametaphosphate used in the roughing is 100 g / t, the amount of copper sulfate used is 150 g / t, the amount of butyl xanthate used is 150 g / t, and the amount of pine oil used is 20 g / t;

[0036] (5) The silver tailings 2 after silver is recovered by magnetic flotation are subjected to manganese flotation by adding a pH adjuster, an inhibitor and a collector. The flotation process is one roughing, three fines and three sweeps to obtain manganese concentrate. The pH adjuster is sodium carbonate, the inhibitor is water glass, the activator is aluminum sulfate, and the collector is oleic acid. The amount of sodium carbonate used in the roughing is 1500 g / t, the amount of water glass used is 2000 g / t, the amount of aluminum sulfate used is 100 g / t, and the amount of oleic acid used is 300 g / t.

[0037] Silver-manganese ore was separated according to the mineral processing steps of the present invention. The results obtained in this embodiment were: the yield of silver concentrate 1 was 1.61%, the Ag grade was 7580 g / t, and the Ag recovery rate was 24%; the yield of silver concentrate 2 was 4.87%, the Ag grade was 6711 g / t, and the Ag recovery rate was 64.23%; the combined yield of silver concentrate 1 and silver concentrate 2 was 6.48%, the combined Ag grade was 6927 g / t, and the combined Ag recovery rate was 88.23%; the yield of manganese concentrate was 26.50%, the Mn grade was 19.89%, and the Mn recovery rate was 72.70%.

[0038] Example 2

[0039] A silver-manganese ore contains Ag 580g / t and Mn 5.15%. The main mineral components are argentite, sideromanganese ore, quartz and dolomite.

[0040] (1) Use jaw crusher and cone crusher to crush the raw ore to less than 6mm;

[0041] (2) The crushed product is fed into a dry magnetic separation device for magnetic separation pretreatment. Through two stages of magnetic separation, namely roughing separation and sweeping separation, a magnetic product containing silver and manganese and a non-magnetic product containing silver are obtained respectively. The magnetic field strength of the first stage is 560 kA / m, and the magnetic field strength of the second stage is 750 kA / m.

[0042] (3) Non-magnetic products and magnetic products are ground separately. Specifically, the grinding fineness of non-magnetic minerals is -0.074mm, accounting for 75%, and the grinding fineness of magnetic materials is 85%;

[0043] The non-magnetic material after grinding treatment was subjected to silver flotation by adding a depressant, an activator, a collector and a frother. The flotation process was one roughing, two finishing and two scavenging, to obtain a silver concentrate 1 and a silver tailing 1. The depressant was water glass, the activator was copper sulfate, the collector was amyl xanthate, and the frother was pine oil. The amount of water glass used in the roughing was 1000 g / t, the amount of copper sulfate used was 100 g / t, the amount of amyl xanthate used was 100 g / t, and the amount of pine oil used was 10 g / t.

[0044] (4) The magnetic material after grinding treatment is subjected to silver flotation by adding an inhibitor, an activator, a collector and a frother. The flotation process is one coarse, two fine and two scavenging, and a silver concentrate 2 and a silver tailing 2 are obtained. The inhibitor is carboxymethyl cellulose, the activator is copper sulfate, the collector is amyl xanthate, and the frother is pine oil. In the coarse selection, the amount of carboxymethyl cellulose used is 300 g / t, the amount of copper sulfate used is 150 g / t, the amount of amyl xanthate used is 200 g / t, and the amount of pine oil used is 20 g / t;

[0045] (5) The silver tailings 2 after silver is recovered by magnetic flotation are subjected to manganese flotation by adding a pH adjuster, an inhibitor and a collector. The flotation process is one roughing, three fines and three sweeps to obtain manganese concentrate. The pH adjuster is sodium carbonate, the inhibitor is sodium hexametaphosphate, the activator is aluminum sulfate, and the collector is oleic acid. The amount of sodium carbonate used in the roughing is 2000 g / t, the amount of sodium hexametaphosphate used is 150 g / t, the amount of aluminum sulfate used is 200 g / t, and the amount of oleic acid used is 250 g / t.

[0046] Silver-manganese ore was separated according to the mineral processing steps of the present invention. The results obtained in this embodiment were: the yield of silver concentrate 1 was 2.58%, the Ag grade was 7558 g / t, and the Ag recovery rate was 33.62%; the yield of silver concentrate 2 was 4.59%, the Ag grade was 6719 g / t, and the Ag recovery rate was 53.17%; the combined yield of silver concentrate 1 and silver concentrate 2 was 7.17%, the combined Ag grade was 7021 g / t, and the combined Ag recovery rate was 86.79%; the yield of manganese concentrate was 19.92%, the Mn grade was 17.21%, and the Mn recovery rate was 66.57%.

[0047] Example 3

[0048] A silver-manganese ore contains 320g / t of Ag and 12.81% of Mn. The main mineral components are argentite, sideromanganese ore, quartz and dolomite.

[0049] (1) Use jaw crusher and cone crusher to crush the raw ore to less than 5mm;

[0050] (2) The crushed product is fed into a dry magnetic separation device for magnetic separation pretreatment. Through two stages of magnetic separation, namely roughing magnetic separation and sweeping magnetic separation, a magnetic product containing silver and manganese and a non-magnetic product containing silver are obtained respectively. The magnetic field strength of the first stage is 600 kA / m, and the magnetic field strength of the second stage is 800 kA / m.

[0051] (3) Non-magnetic products and magnetic products are ground separately. Specifically, the grinding fineness of non-magnetic minerals is -0.074mm, accounting for 75%, and the grinding fineness of magnetic materials is 90%;

[0052] The non-magnetic material after grinding was subjected to silver flotation by adding a depressant, an activator, a collector, and a frother. The flotation process was one roughing, two finishing, and two scavenging, to obtain silver concentrate 1 and silver tailing 1. The depressant was sodium hexametaphosphate, the activator was copper sulfate, the collector was butyl xanthate, and the frother was pine oil. The dosage of sodium hexametaphosphate in the roughing was 60 g / t, the dosage of copper sulfate was 80 g / t, the dosage of butyl xanthate was 80 g / t, and the dosage of pine oil was 15 g / t.

[0053] (4) The magnetic material after grinding treatment is subjected to silver flotation by adding an inhibitor, an activator, a collector and a frother. The flotation process is one coarse, two fine and two scavenging, and a silver concentrate 2 and a silver tailing 2 are obtained. The inhibitor is water glass, the activator is copper sulfate, the collector is butyl xanthate, and the frother is pine oil. The amount of water glass used in the coarse selection is 1500 g / t, the amount of copper sulfate used is 200 g / t, the amount of butyl xanthate used is 180 g / t, and the amount of pine oil used is 20 g / t;

[0054] (5) The silver tailings 2 after silver is recovered by magnetic flotation are subjected to manganese flotation by adding a pH adjuster, an inhibitor and a collector. The flotation process is one roughing, three fines and three sweeps to obtain manganese concentrate. The pH adjuster is sodium carbonate, the inhibitor is water glass, the activator is aluminum sulfate, and the collector is oleic acid. The amount of sodium carbonate used in the roughing is 1800 g / t, the amount of water glass used is 2000 g / t, the amount of aluminum sulfate used is 300 g / t, and the amount of oleic acid used is 400 g / t.

[0055] Silver-manganese ore was separated according to the mineral processing steps of the present invention. The results obtained in this embodiment were: the yield of silver concentrate 1 was 1.26%, the Ag grade was 5735 g / t, and the Ag recovery rate was 22.58%; the yield of silver concentrate 2 was 4.31%, the Ag grade was 4826 g / t, and the Ag recovery rate was 65%; the combined yield of silver concentrate 1 and silver concentrate 2 was 5.57%, the combined Ag grade was 5032 g / t, and the combined Ag recovery rate was 87.58%; the yield of manganese concentrate was 37.56%, the Mn grade was 23.87%, and the Mn recovery rate was 69.99%.

[0056] Comparative Example 1

[0057] Comparative Example 1 and Example 1 processed the same raw materials, except that the comparative example adopted a flotation silver separation and tailings magnetic separation process for manganese separation. The silver separation process was a one-roughing, one-sweeping, two-fine separation process. The flotation reagents were water glass, copper sulfate, butyl xanthate, and pine oil. In the roughing separation, the amount of water glass used was 1500 g / t, the amount of copper sulfate used was 200 g / t, the amount of butyl xanthate used was 200 g / t, and the amount of pine oil used was 30 g / t. The manganese magnetic separation used a high-gradient magnetic separator with a two-stage magnetic separation process, one coarse and one sweep, with magnetic field intensities of 960 kA / m and 1120 kA / m, respectively.

[0058] The results obtained in this comparative example are: the silver concentrate yield is 6.40%, the Ag grade is 6373g / t, and the Ag recovery rate is 80.07%; the manganese concentrate yield is 43.92%, the Mn grade is 11.69%, and the Mn recovery rate is 70.82%.

[0059] Comparative Example 2

[0060] Comparative Example 2 and Example 1 process the same raw materials, except that the comparative example adopts a flotation process for silver selection and tailings flotation for manganese selection. The silver selection process is a one-roughing, one-scavenging, two-refining process. The flotation reagents are water glass, copper sulfate, butyl xanthate, and pine oil. The amount of water glass used in the roughing process is 1500 g / t, the amount of copper sulfate used is 200 g / t, the amount of butyl xanthate used is 200 g / t, and the amount of pine oil used is 30 g / t. The manganese selection process is a one-roughing, three-refining, and three-scavenging process. The pH adjuster is sodium carbonate, the depressant is water glass, the activator is aluminum sulfate, and the collector is oleic acid. The amounts of sodium carbonate used in the roughing process are 2000 g / t, 2000 g / t of water glass, 200 g / t of aluminum sulfate, and 300 g / t of oleic acid.

[0061] The results obtained in this comparative example are: the silver concentrate yield is 6.27%, the Ag grade is 6526g / t, and the Ag recovery rate is 80.39%; the manganese concentrate yield is 29.09%, the Mn grade is 15.34%, and the Mn recovery rate is 61.55%.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for separating and recovering silver and manganese from silver-manganese ore, characterized in that: The following steps are involved: (1) crushing the silver-manganese ore to obtain a crushed product; (2) pre-treating the crushed product by dry magnetic separation to obtain a magnetic product containing silver and manganese and a non-magnetic product containing silver; (3) flotation-recovering silver from the non-magnetic product to obtain a silver concentrate 1 and a silver tailing 1; (4) flotation-recovering silver from the magnetic product to obtain silver concentrate 2 and silver tailings 2; (5) flotation is performed on the silver tailings 2 to recover manganese to obtain manganese concentrate and manganese tailings.

2. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 1, wherein: In step (3) and step (4), the non-magnetic product and the magnetic product need to be ground before flotation to recover silver, and the grinding fineness is -0.074mm, accounting for 70%-90%.

3. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 1, wherein: In step (1), the upper limit of the crushing particle size is 5-8 mm.

4. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 1, wherein: In step (2), the magnetic field strength of the dry magnetic separation is 500-800 kA / m.

5. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 1, wherein: In step (3) and step (4), the flotation recovery of silver includes a roughing stage, 2-3 cleaning stages and 2-3 scavenging stages. The roughing stage obtains a silver concentrate, and the silver concentrate is subjected to 2-3 cleaning stages to obtain silver concentrate 1 or silver concentrate 2.

6. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 1, wherein: In step (5), flotation recovery of manganese includes a roughing process, 2-3 cleaning processes and 2-3 scavenging processes, wherein the roughing process obtains a manganese concentrate, and the manganese concentrate is subjected to 2-3 cleaning processes to obtain a manganese concentrate.

7. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 5, characterized in that: In step (3) and step (4), silver is recovered by flotation by adding an inhibitor, an activator, a collector and a frother, wherein the inhibitor is water glass, sodium hexametaphosphate or carboxymethyl cellulose, the activator is copper sulfate or lead nitrate, the collector is one or more of butyl xanthate, amyl xanthate and butyl ammonium black medicine, and the frother is pine oil or methyl isobutyl carbinol.

8. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 6, wherein: In step (5), manganese is recovered by flotation by adding a pH adjuster, an inhibitor, an activator and a collector for manganese flotation, wherein the pH adjuster is one or more of sodium carbonate, sodium hydroxide and lime, the inhibitor is water glass, sodium hexametaphosphate or carboxymethyl cellulose, the activator is aluminum sulfate, and the collector is one or more of oleic acid, oxidized paraffin soap or sodium petroleum sulfonate.

9. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 1 or 4, characterized in that: In step (2), the dry magnetic separation includes two stages of magnetic separation: roughing magnetic separation and scavenging magnetic separation. The magnetic field strength of the roughing magnetic separation is 500-600 kA / m, and the magnetic field strength of the scavenging magnetic separation is 700-800 kA / m.

10. The method for separating and recovering silver and manganese from silver-manganese ore according to claim 1, characterized in that: In step (1), the silver-manganese ore contains 300-600 g / t of Ag and 5-15 wt.% of manganese, and the silver minerals are embedded in the iron-manganese carbonate minerals and quartz minerals in the form of fine particles.

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