1. A full‑flotation beneficiation method for simple siderite ore, characterized in that it is carried out by the following steps: after crushing and grinding the siderite feed, one stage of roughing and three stages of cleaning are performed;

• Roughing: sodium hexametaphosphate is added as a regulator at a dosage of 300–600 g/t to improve pulp dispersion, with stirring for 3–6 min; sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added as a depressant at a dosage of 500–800 g/t, with stirring for 3–6 min; an SP‑type siderite collector is added at a dosage of 400–800 g/t, with stirring for 3–6 min; No. 2 oil is added as a frother at a dosage of 10–40 g/t, with stirring for 3–6 min; then air is introduced and froth is scraped to obtain froth product I, which proceeds to the next cleaning stage;
• Cleaning I: sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added at 300–500 g/t, with stirring for 3–6 min; No. 2 oil is added at 10–30 g/t, with stirring for 3–6 min; air is introduced and froth is scraped to obtain froth product II, which proceeds to the next cleaning stage;
• Cleaning II: sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added at 200–400 g/t, with stirring for 3–6 min; No. 2 oil is added at 10–20 g/t, with stirring for 3–6 min; air is introduced and froth is scraped to obtain froth product III, which proceeds to the next cleaning stage;
• Cleaning III: sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added at 100–300 g/t, with stirring for 3–6 min; No. 2 oil is added at 5–10 g/t; air is introduced and froth is scraped; the froth product is dewatered and dried to obtain the final siderite concentrate.

2. The full‑flotation beneficiation method for simple siderite ore according to claim 1, characterized in that said crushing and grinding comprises crushing the siderite feed to below 3 mm, homogenizing it, and grinding it in a ball mill at a liquid‑to‑solid weight ratio of 1:2 to a fineness such that the –0.074 mm fraction accounts for 75%–95% and the –0.100 mm fraction accounts for 100%.

3. The full‑flotation beneficiation method for simple siderite ore according to claim 1, characterized in that said dewatering and drying comprises drying the froth product until the moisture content by weight is below 5%.

単純なシデライト鉱石のためのフルフロテーション選鉱法

I. Technical Field
The present invention relates to a full-flotation beneficiation method for simple siderite ore, belonging to the technical field of mineral processing engineering for iron ores. It is particularly applicable to the beneficiation of ores in which siderite is the main mineral, associated with hematite–limonite, pyrrhotite, pyrite, etc.

II. Background Art
Among proven iron ore reserves, although siderite (including simple siderite, hematite, limonite, siderite–limonite associations, etc.) accounts for less than 10% of the world’s reserves, forecasts indicate that in potential world iron ore resources, siderite accounts for more than 40%. China has relatively abundant siderite resources, with reserves ranking among the top in the world, totalling about 1.834 billion tonnes. Because siderite has a very fine dissemination size, complex composition, and low grade, iron mainly occurs in carbonate form. Part of the siderite, due to the substitution of Fe²⁺ by Mg²⁺ and Mn²⁺, forms magnesium–manganese siderite as isomorphous mixtures, and is hosted in hematite–limonite and magnetite. Limonite has low grade and is complex and refractory, making it difficult to improve iron grade and recovery; moreover, it tends to produce slime during grinding, which affects the beneficiation index. At present, siderite, limonite, and associated complex low‑grade iron ores are widely recognized as difficult beneficiation challenges. To fully develop low‑grade siderite resources dominated by siderite, abroad, conventional physical beneficiation processes such as gravity separation, high‑intensity magnetic separation, flotation, roasting, etc., either singly or in combination, are often used. In the 1950s and 1960s, several Eastern European countries built semi‑industrial siderite concentrators, but all suffered from generally low techno‑economic indices. For example, the Bakal concentrator in Ukraine, which used a roasting process, could only achieve a concentrate grade of up to 53%; another example is the Czech Děčín concentrator, which used a magnetic‑flotation combined flowsheet and produced an iron concentrate grade of only about 35%. In Germany, the Siegerland plant treated manganese‑bearing siderite and obtained an iron concentrate grade of 50% with a recovery of 62.8% (see “Beneficiation technology for carbonate iron ores containing magnesium oxide,” Foreign Metal Ore Dressing, 1975, 7: 4652). To date, there is no industrial practice for simple siderite ores either domestically or internationally. Even though some associated siderite can be comprehensively recovered in iron ore processing flowsheets at Daye Iron Mine and Jiuquan Iron Mine, the siderite concentrate obtained contains only about 35% iron.

Siderite is a carbonate‑type mineral, and after roasting its iron grade increases significantly. Although the roasting process can yield an iron concentrate with a relatively high grade, it involves two roasting stages (one magnetizing roasting and one sintering), resulting in very high costs. If conventional physical beneficiation methods can enrich the iron grade to about 39%, and then the product is pelletized and sintered, the iron grade can be raised to about 55%, thereby eliminating one roasting step and reducing roasting costs, with correspondingly improved economic benefits. Similarly, high‑intensity magnetic separation consumes large amounts of electricity and water, has high costs, and is difficult to industrialize. At present, there is no successful practical experience with full‑flotation for siderite, mainly due to difficulties in selecting effective siderite collectors.

III. Summary of the Invention
The present invention provides a full‑flotation beneficiation method for simple siderite ore. For simple siderite ores with small amounts of associated hematite–limonite, pyrrhotite, pyrite, etc., a full‑flotation flowsheet is adopted, which can yield a siderite concentrate with a grade of TFe ≥ 38% and an iron recovery of 75–86%. The full‑flotation flowsheet provided by the present invention uses a siderite collector that causes strong physicochemical adsorption on the surface of siderite, thereby achieving effective separation of siderite from other minerals.

The full‑flotation flowsheet for siderite according to the present invention comprises the following steps:

(1) Crushing and grinding of feed: The siderite feed is crushed to below 3 mm and homogenized. It is then ground in a ball mill at a liquid‑to‑solid ratio (by weight) of 1:2. The grinding fineness is such that the –0.074 mm fraction accounts for 75–95% and the –0.100 mm fraction accounts for 100%.

(2) Flotation stages: One stage of roughing and three stages of cleaning are carried out for siderite.

• Siderite roughing: Sodium hexametaphosphate is added as a regulator at 300–600 g/t to improve pulp dispersion, with stirring for 3–6 min; sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added as depressant at 500–800 g/t, with stirring for 3–6 min; the SP‑type high‑efficiency siderite collector is added at 400–800 g/t, with stirring for 3–6 min; No. 2 oil is added as frother at 10–40 g/t, with stirring for 3–6 min; then air is introduced and froth is scraped to obtain froth product I, which proceeds to the next cleaning stage.
• Siderite cleaning I: Sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added at 300–500 g/t, with stirring for 3–6 min; No. 2 oil is added at 10–30 g/t, with stirring for 3–6 min; air is introduced and froth is scraped to obtain froth product II, which proceeds to the next cleaning stage.
• Siderite cleaning II: Sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added at 200–400 g/t, with stirring for 3–6 min; No. 2 oil is added at 10–20 g/t, with stirring for 3–6 min; air is introduced and froth is scraped to obtain froth product III, which proceeds to the next cleaning stage.
• Siderite cleaning III: Sulfuric acid is used to adjust pH to 5–6, with stirring for 3–6 min; starch is added at 100–300 g/t, with stirring for 3–6 min; No. 2 oil is added at 5–10 g/t; air is introduced and froth is scraped. The froth product is dewatered and dried to obtain the final siderite concentrate.

The SP‑type collector has been disclosed in patent application No. 200810058134.3, and its formulation and preparation process are as follows:

Raw materials:

• S₁: dodecylamine
• S₂: mixed amine
• S₃: ether amine
• S₄: naphthenic acid (CₙH₂ₙ₋₁COOH)
• P₁: sulfuric acid
• P₂: hydrochloric acid
• P₃: caustic soda (sodium hydroxide)

Weight ratios:

• S = dodecylamine S₁ : mixed amine S₂ : hydrochloric acid P₂ = 20–40 : 20–40 : 80–20
• P = ether amine S₃ : naphthenic acid S₄ : caustic soda P₃ : sulfuric acid P₁ = 10–30 : 20–50 : 10–20 : 60–10
• SP = S : P = 10–80 : 90–20

The purity of dodecylamine is ≥96%, mixed amine ≥95%, hydrochloric acid concentration ≥35% by weight; sulfuric acid concentration ≥95% by weight, caustic soda purity ≥96%, ether amine purity ≥98%, naphthenic acid purity ≥98%.

The SP collector is prepared according to the above formulation by the following method:

• Preparation of S: According to the weight ratio, divide hydrochloric acid P₂ into two equal portions. Mix one portion with dodecylamine S₁ with stirring and age for 20 min; mix the other portion with mixed amine S₂ with stirring and age for 20 min; then combine the two mixtures, stir for 5 min, and allow to stand at room temperature and atmospheric pressure for aging for 20 min.
• Preparation of P: According to the weight ratio, first mix ether amine S₃ and naphthenic acid S₄ uniformly and age for 5 min to obtain a mixture; then mix the mixture with caustic soda P₃ and then with sulfuric acid P₁, stirring uniformly, and age for 10 min.
• Preparation of SP: According to the weight ratio, add S and P together, stir uniformly, and allow to stand for 20 min until the temperature cools to room temperature to obtain the collector product.

Compared with known technologies, the present invention has the following advantages and positive effects: For simple siderite ores with small amounts of associated hematite–limonite, pyrrhotite, pyrite, etc., the full‑flotation flowsheet can yield a siderite concentrate with TFe ≥ 38% and an iron recovery of 75–86%. The full‑flotation flowsheet provided by the present invention uses a siderite collector that allows strong physicochemical adsorption on the siderite surface, enabling effective separation of siderite from other minerals.

IV. Brief Description of the Drawings
Figure 1 is the process flowsheet of the present invention.

V. Detailed Description of the Embodiments

例 1
The siderite sample came from a certain area in Yunnan Province. The raw ore did not exceed the limits for sulfur, phosphorus, or arsenic. The main recoverable element was iron, and other elements did not reach values for comprehensive recovery. The mineral content and chemical composition of the raw ore are shown in Tables 1 and 2, respectively. Using the full‑flotation flowsheet shown in Figure 1, the siderite was crushed to below 3 mm and homogenized. It was ground in a ball mill at a liquid‑to‑solid ratio of 1:2 to a fineness of –0.074 mm occupying 85.38%. The flotation reagent scheme was:
(1) Siderite roughing: sodium hexametaphosphate 300 g/t, stirring for 4 min; sulfuric acid to pH 5–6, stirring for 4 min; SP collector 600 g/t, stirring for 3 min; starch 600 g/t, stirring for 3 min; No. 2 oil 40 g/t, stirring for 3 min; aeration and froth scraping.
(2) Siderite cleaning I: starch 300 g/t, stirring for 3 min; No. 2 oil 20 g/t, stirring for 3 min; aeration and froth scraping.
(3) Siderite cleaning II: sulfuric acid to pH 5–6; starch 200 g/t, stirring for 3 min; No. 2 oil 15 g/t, stirring for 3 min; aeration and froth scraping.
(4) Siderite cleaning III: sulfuric acid to pH 5–6; starch 100 g/t, stirring for 3 min; No. 2 oil 6 g/t, stirring for 3 min; aeration and froth scraping.
The froth product was dewatered and dried to a moisture content below 5% by weight to obtain the siderite concentrate. The achieved indices are shown in Table 3.

Equipment used: ball mill Φ900×1800 mm, jaw crushers Φ10×50 mm and Φ3×30 mm, self‑aeration flotation cells (single cell volume 3 m³) manufactured by Kunming Ciba Mining Machinery Factory, spiral classifier Φ2000 mm, hydrocyclone Φ150 mm.

Table 1 Mineral composition of the raw ore

Table 2 Chemical analysis of the raw ore

Table 3 Beneficiation indices of the flowsheet

例 2
The siderite sample came from a certain area in Yunnan Province. The raw ore did not exceed the limits for sulfur, phosphorus, or arsenic. The main recoverable element was iron, and other elements did not reach values for comprehensive recovery. The mineral content and chemical composition of the raw ore are shown in Tables 4 and 5, respectively. Using the full‑flotation flowsheet of Figure 1, the grinding fineness was –0.074 mm occupying 88.78%. The reagent scheme was:
(1) Siderite roughing: sodium hexametaphosphate 400 g/t; sulfuric acid to pH 5–6; SP collector 700 g/t; starch 600 g/t; No. 2 oil 40 g/t; aeration and froth scraping.
(2) Siderite cleaning I: starch 400 g/t; No. 2 oil 20 g/t; aeration and froth scraping.
(3) Siderite cleaning II: sulfuric acid to pH 5–6; starch 200 g/t; No. 2 oil 15 g/t; aeration and froth scraping.
(4) Siderite cleaning III: sulfuric acid to pH 5–6; starch 200 g/t; No. 2 oil 6 g/t; aeration and froth scraping.
The indices are shown in Table 6.

Table 4 Mineral composition of the raw ore

Table 5 Chemical analysis of the raw ore

表6 Beneficiation indices of the flowsheet

例 3
The siderite sample came from a certain area in Gansu Province. The raw ore did not exceed the limits for sulfur, phosphorus, or arsenic. The main recoverable element was iron, and other elements did not reach values for comprehensive recovery. The mineral content and chemical composition of the raw ore are shown in Tables 7 and 8, respectively. Using the full‑flotation flowsheet of Figure 1, the grinding fineness was –0.074 mm occupying 81.68%. The reagent scheme was:
(1) Siderite roughing: sodium hexametaphosphate 400 g/t; sulfuric acid to pH 5–6; SP collector 700 g/t; starch 600 g/t; No. 2 oil 40 g/t; aeration and froth scraping.
(2) Siderite cleaning I: starch 400 g/t; No. 2 oil 20 g/t; aeration and froth scraping.
(3) Siderite cleaning II: sulfuric acid to pH 5–6; starch 200 g/t; No. 2 oil 15 g/t; aeration and froth scraping.
(4) Siderite cleaning III: sulfuric acid to pH 5–6; starch 200 g/t; No. 2 oil 6 g/t; aeration and froth scraping.
The beneficiation indices are shown in Table 9.

表7 Mineral composition of the raw ore

表8 Chemical analysis of the raw ore

表9 Beneficiation indices of the flowsheet