AU2020463690B2 - Method for recycling multiple valuable metals from lateritic nickel ore and regeneration cycle of acid-alkaline double medium - Google Patents

Abstract

A method for recycling multiple valuable metals from lateritic nickel ore and regeneration cycle of an acid-alkali double medium, comprising: first, finely grinding raw lateritic nickel ores to obtain ore powder, configuring the ore powder into slurry and then performing nitric acid leaching on same, and performing a pelletized sintering process on leach residues to obtain iron ore concentrate; adjusting a pH value of a leach solution, completely precipitating aluminum, nickel, cobalt, manganese, scandium, and a small amount of iron, and dissolving precipitates using alkali to separate aluminum; performing acidolysis on a mixture of nickel, cobalt, manganese, and scandium precipitates, then performing fractional extraction on the mixture to obtain scandium, nickel, cobalt, and manganese products; and concentrating, by evaporation, a magnesium nitrate solution obtained after aluminum, nickel, cobalt, manganese, and scandium are precipitated to obtain a magnesium nitrate crystal for subsequently decomposing magnesium nitrate and regenerating to obtain acid and alkali, thereby achieving regeneration cycle of an acid-alkali double medium. The method avoids, in a process of adding an alkaline substance to a lateritic nickel ore acid leach solution to precipitate aluminum for separating aluminum from nickel and cobalt, the problems that during recycling, the filterability is poor and nickel and cobalt metals are included in aluminum slags due to the generation of flocculent aluminum hydroxide precipitates, such that a total recovery rate of nickel and cobalt metals is improved.

Description

Description

Method for recovering valuable metals from a laterite-nickel ore and regenerating and recycling two mediums of acid and alkaline

Field The present invention relates to a crossing field of metallurgy and chemical engineering, and particularly to a method for recovering valuable metals from a laterite-nickel ore and regenerating and recycling two mediums of acid and alkaline.

Background Aluminum, nickel, cobalt metals are very commonly used metals in industrial and civil industries. In particular, nickel metal is mainly used in strainless steel, alloy steel, special alloy and the like. As nickel sulfide ore resources continuously decrease, it becomes a research focus to efficiently and economically extract valuable metals from a laterite-nickel ore because the laterite-nickel ore accompanies with cobalt. The process for treating a laterite-nickel ore is classified into a pyrogenic process and a wet process. The pyrogenic process is mainly suitable for treating a nickel sulfide ore and a laterite-nickel ore containing a high content of nickel. The wet process is suitable for treating a mineral containing a low content of nickel such as a limonitic laterite-nickel ore. The wet process has advantages of less energy consumption, low cost, less pollution and the ability of recovering cobalt at the same time. Currently, the wet process for refining a laterite-nickel ore mainly comprises a normal pressure acid leaching process and a pressure acid leaching process, in whichever process, elements such as Co, Mn, Al, Fe, and Mg will exist in the acid leaching solution. In prior art, the metal elements in the acid leaching solution are typically extracted by adding an alkaline material such as magnesium oxide to adjust the pH value. The impurity of aluminium hydroxide iron residue is first precipitated and separated at pH 3-4, and then the crude products of nickel, cobalt and manganese hydroxides is precipitated at pH 7-9. Then, the acid leaching process is used in combination with technologies such as extraction, electrolysis and evaporation concentration to purify the final products of nickel and cobalt, such as nickel sulfate, cobalt sulfate, electrolytic nickel, and electrolytic cobalt. However, during the precipitation and separation of the aluminum metal, the problem of poor filtering performance of the aluminium hydroxide residue due to the occurrence of flocculent aluminum hydroxide precipitatea often arises, and the precipitated aluminium hydroxide residue will entrain more nickel and cobalt metal elements, resulting in some loss in the recovery of the nickel and cobalt metals. Also, the nitric acid is expensive, and the pH adjustment needs a large amount of alkaline (MgO). If the recovery is not taken into consideration, the economic benefit of the process will be significantly decreased. The Chinese Patent CN108950205B discloses a method comprising finely grinding alkaline materials of calcium carbonate and magnesium carbonate, well mixing them with water, then adding the mixture into a mixing tank at a controlled flow rate simultaneously with an acid leaching solution, to control the pH value of the solution so as to homogeneously precipitate an aluminum iron residue. Although this method improves the filtering performance of the precipitate to some extent, the contents of the nickel and cobalt metals are still around 1-2%, resulting in loss in the recovery of the nickel and cobalt metals.

Summary In view of the defects and deficiencies in prior art, the present invention provides a method for recovering valuable metals from a laterite-nickel ore and regenerating and recycling two mediums of acid and alkaline. In the method, the process is efficient and simple, and the problems of poor filtering performance in the recovery due to the generation of flocculent aluminum hydroxide precipitate and the entrainment of nickel and cobalt metals in the aluminum slag are avoided during the precipitation of aluminum and the separation of cobalt and nickel by adding an alkaline material into the nitric acid leaching solution of the laterite-nickel ore, thereby increasing the total recovery of nickel and cobalt metals. Meanwhile, the magnesium nitrate solution after precipitating aluminum, nickel, cobalt, manganese and scandium is subjected to evaporation concentration to obtain a magnesium nitrate crystal, which is used for subsequent magnesium nitrate decomposition and regeneration to obtain an acid (nitric acid) and an alkaline (magnesium oxide), thereby achieving the regeneration and recycling of two mediums of acid and alkaline. This process has good adaptability to raw materials, and is particularly suitable for a limonitic laterite-nickel ore containing a high content of aluminum. The present invention is achieved by the following technical solutions. A method for recovering valuable metals from a laterite-nickel ore and regenerating and recycling two mediums of acid and alkaline, comprising steps of: (1) crushing and finely grinding a raw laterite-nickel ore to obtain mineral powders, and mixing and well stirring the mineral powders and nitric acid to prepare a mineral slurry; (2) pumping the mineral slurry into an autoclave for a leaching reaction, pre-neutralizing the mineral slurry to adjust a pH value of the mineral slurry after the reaction, and then subjecting the mineral slurry to a multistage thickening washing to obtain an underflow and an overflow liquid;

(3) subjecting the underflow to filtering, drying and pellet sintering to obtain an iron ore concentrate, and subjecting the overflow liquid to a precipitation reaction by adjusting a pH value of the overflow liquid, such that aluminum, nickel, cobalt, manganese, scandium and a minor amount of iron in an acid leaching solution are completely precipitated and separated from a magnesium nitrate solution after the reaction, and filtering out the aluminum, nickel, cobalt, manganese, scandium and a minor amount of iron to obtain a first precipitation filter residue; (4) adding an alkaline to the first precipitation filter residue to convert aluminium hydroxide in the filter residue to an aluminate ion which is then dissolved in an alkaline solution, filtering the resultant mixture to obtain a second precipitation filter residue; and adding a carbon dioxide or aluminium hydroxide seed crystal in a filtrate obtained after filtering for precipitation to obtain a product of aluminum hydroxide; and (5) dissolving the second precipitation filter residue with sulfuric acid, then extracting scandium, stripping the scandium, and crystalizing the scandium to produce a scandium slat, using a liquid obtained after extracting scandium for preparing a nickel-cobalt-manganese ternary material, or subjecting the liquid to fractional extraction, stripping and crystallization to produce products of nickel, cobalt, and manganese. Further, in Step (1), the laterite-nickel ore is a typical limonitic high iron and low nickel ore, with a chemical composition of: 0.5-2.0 mass% of Ni; 0.05-0.20 mass% of Co; 35-55 mass% of Fe; 0.5-5.0 mass% of Al; 0.1-3.0 mass% of Mn; 0.50-5.0 mass% of Mg; and 30-130 g/t of Sc. Further, in Step (1), the nitric acid is at a concentration of 120-230 g/L, and a solid liquid ratio of a mixture of the mineral powders and the nitric acid is 1:0.5-1:5 g/ml. Further, in Step (2), the autoclave in Step (2) is equipped with a stirrer which stirs the mineral slurry during leaching at a stirring speed of

150-250 rpm; and the leaching reaction is performed at a leaching temperature of 160-220°C for a leaching period of 0.5-3 h. Further, in Step (2), magnesium oxide is added to the mineral slurry after the leaching reaction for pre-neutralization to adjust the pH value of the mineral slurry to 2.5-3.5. Further, in Step (3), magnesium oxide is added to the overflow liquid to adjust the pH value of the overflow liquid to 7.0-10.0; and the precipitation reaction is performed at a reaction temperation of 40-100°C for a reaction period of 0.5-3.5 h. Further, in Step (4), adding the alkaline to the first precipitation filter residue for dissolving is performed at a reaction temperature of 140-200°C for a reaction period of 1-4 h at a pH value in a range of 12.5-14.0; and the alkaline used comprises any one of sodium hydroxide and potassium hydroxide or a combination thereof. Further, Step (4) further comprises adding the carbon dioxide or aluminum hydroxide seed crystal to the filtrate obtained after filtering out the second precipitation filter residue to obtain a product of aluminum hydroxide. Further, in Step (5), dissolving the second precipitation filter residue with sulfuric acid is perfomred at a reaction temperature of 30-100°C for a reaction period of 1.0-2.5 h at a pH in a range of 0.5-3.5. Further, in Step (5), the scandium salt comprises any one of scandium oxalate, scandium nitrate and scandium chloride, but is not limited to these, and thus these are collectively called scandium salt. Further, Step (5) further comprises pyrolyzing the scandium salt produced at a heating temperature of 300°C-800°C to obtain scandium oxide, and the pyrolyzing comprises any one of calcination pyrolysis, spray pyrolysis and suspension boiling pyrolysis, or a combination thereof; and the product of scandium oxide may be sold as a commodity.

The above method further comprises the regeneration and recycling of two mediums of acid and alkaline, comprising steps of: (6) subjecting a first precipitation filtrate to evaporation concentration to obtain a magnesium nitrate crystal, which is then heated and melted and sent to a decomposing furnace for pyrolysis to form a high temperature dust gas; (7) separating magnesium oxide powders from the high temperature dust gas through a dust collecting system, and returning the magnesium oxide produced to the first precipitation procedure; heating a portion of NOx gas obtained after dust collecting through a burner; recycling the heated NOx gas to the burner for pyrolyzing magnesium nitrate; sending the other portion of NOx to a nitric acid regeneration system, and subjecting the NOx to tail gas heat exchange, deep dedusting and twice cooling condensation to obtain a dilute nitric acid, pumping the condensed acid to an absorber, pressurizing and densifying a gas which is not condensed and absorbed through a nitrogen oxide compressor, sending the gas to the absorber to prepare nitric acid, and returning the nitric acid produced to the leaching procedure. Further, in Step (6), the pyrolysis in the decomposing furnace comprises any one of boiling pyrolysis, calcination pyrolysis and spray pyrolysis, but is not limited to the above processes, and a decomposition temperature in the furnace is 400°C-900°C; and the high temperature dust gas comprises magnesium oxide, steam, NOx and oxygen. Further, in Step (7), 20-95% of the NOx gas obtained after dust collecting is heated through the burner, and recycled to the decomposing furnace for pyrolyzing magnesium nitrate. Further, in Step (7), the NOx entered into the nitric acid regeneration system is subjected to a deep dedusting and has its temperature decreased to 120°C or lower when it arrives at a cooling system to obtain a large amount of condensed acid, and the condensed acid is at a concentration of

-35%; the NOx which is not condensed and absorbed is pressurzied to 4.0 MPa-5.0 MPa, and sent to the absorber to be absorbed to prepare nitric acid, during which the previous condensed acid is used as an absorbent, and a tail gas obtained after absorption is discharged after being treated to meet the discharge requirement. The technical solutions of the present invention have advantageous effects as follows: (1) in the present invention, the problem of poor filtering performance of flocculent aluminium hydroxide in conventional processes is avoided, and the the aluminium hydroxide obtained in the present process has a high purity; (2) the overall recovery of the nickel and cobalt metals in the whole course is increased, further increasing the economic benefit of the present process; (3) efficient separation and recovery of aluminum and scandium are achieved, which has a broad application prospect; (4) both acid and alkaline used in the process can be regenerated and recycled, which reduces the purchase of auxiliary materials and reduces direct processing cost; and (5) the condensed acid formed in the process is used in subsequent nitric acid regeneration system to prepare nitric acid, which converts the spent acid to a valuable material, increases the efficiency for nitric acid regeneration, and reduces fixed investment and nitric acid regeneration cost.

Brief Description of Drawings Fig. 1 is a flow chart for a method for recovering valuable metals from a laterite-nickel ore and regenerating and recycling two mediums of acid and alkaline according to the present invention.

Detailed Description The present invention will be described in further detail with reference to the drawings and particular embodiments below, but the protection scope of the present invention is not limited thereto. The present invention discloses a method for recovering valuable metals from a laterite-nickel ore and regenerating and recycling two mediums of acid and alkaline. As shown in Fig. 1, the method comprises the following steps. Firstly, a raw laterite-nickel ore is crushed and finely ground to obtain mineral powders, then the mineral powders are formulated into a slurry for nitric acid high pressure leaching, the leaching slurry obtained has the pH adjusted and is thickening washed to achieve a solid-liquid separation, thereby obtaining a leaching residue and a leaching solution, and the leaching residue is filtered, oven dried, and then subjected to a pellet sintering process to obtain an iron ore concentrate. A magnesium oxide is added to the leaching solution to adjust the pH value of the solution, so as to completely precipitate aluminum, nickel, cobalt, manganese, scandium and a minor amount of iron in the acid leaching solution. Then, with the pH value of the solution and the reaction temperature controlled, the precipitant is dissolved with an alkaline, the aluminium hydroxide in the mixture is converted to aluminate ion which is dissolved in the alkaline solution and is separated from the precipitate of nickel, cobalt, manganese and scandium through filtering. A carbon dioxide or aluminium hydroxide seed crystal is added into the alkaline solution for precipitation to obtain a product of aluminium hydroxide. The precipitate mixture of nickel, cobalt, manganese and scandium is dissolved with sulfuric acid, then scandium is extracted, stripped and crystallized to produce a scandium salt, and the scandium salt is pyrolyzed to obtain scandium oxide which is sold as a commodity. Then, manganese/cobalt/nickel are subjected to fractional exatraction, stripping and crystallization to obtain products of nickel, cobalt and manganese. The magnesium nitrate solution obtained after precipitating aluminum, nickel, cobalt, manganese and scandium is subjected to evaporation concentration to obtain a magnesium nitrate crystal, and the magnesium nitrate crystal is heated to be melted, and then added to the decomposing furnace. The magnesium nitrate melt is rapidly decomposed under heat to form magnesium oxide, NO, 0 2, and the like. The dust-containing gas passes through a dedusting system to obtain a high purity active magnesium oxide, a portion of the NOx gas obtained after dedusting is heated through a burner, and then enters into the decomposing system again for pyrolyzing the magnesium nitrate melt, and the other portion of the NOx gas is cooled and flows to a nitric acid regeneration system to prepare nitric acid. The gas entering into the nitric acid regeneration system is subjected to tail gas heat exchange, deep dedusting and twice cooling condensation to obtain a condensed dilute nitric acid. The subsequent gas is pressurized and densified by a nitrogen oxide compressor, and enters into an absorber. After measuring the concentration, the condensed acid obtained by the previous condensation is pumped to respective trays of a nitric acid absorber for preparing nitric acid. The industrial nitric acid produced by the nitric acid regeneration system will be used in the front-end leaching procedure, and the high purity active magnesium oxide obtained is used in the front-end pH adjustment. In the method, the process is efficient and simple, and the problems of poor filtering performance in the recovery due to the generation of flocculent aluminum hydroxide precipitate and the entrainment of nickel and cobalt metals in the aluminum slag are avoided during the separation of aluminum from cobalt and nickel by adding an alkaline material into the nitric acid leaching solution of the laterite-nickel ore to control the pH value to precipitate aluminum, thereby increasing the total recovery of nickel and cobalt metals. The magnesium nitrate solution after precipitating aluminum, nickel, cobalt, manganese and scandium is subjected to evaporation concentration to obtain a magnesium nitrate crystal, which is used for subsequent magnesium nitrate decomposition and regeneration to obtain an acid (nitric acid) and an alkaline (magnesium oxide), thereby achieving the regeneration and recycling of two mediums of acid and alkaline. Also, this process has good adaptability to raw materials, and is particularly suitable for a limonitic laterite-nickel ore containing a high content of aluminum. Example 1 A raw laterite-nickel ore containing 0.6% of nickel, 0.05% of cobalt, 48% of iron, 1.3% of aluminum, 0.15% of manganese, 0.6% of magnesium, and 43 g/t of scandium was crushed and finely ground to obtain mineral powders as a raw material for subsequent use. The mineral powders, nitric acid, and water were well stirred and mixed at a liquid-solid ratio of 1:5 g/mL and an initial acid concentration of 120 g/L in a slurrying tank to prepare a mineral slurry, and then the mineral slurry was pumped into a nitric acid autoclave for leaching. The leaching was performed at a leaching temperature of 160°C for a leaching period of 1 h at a stirring speed of 170 rpm. After the reaction, magnesium oxide was added into the mineral slurry to pre-neutralize it to adjust the pH to 2.5, and then the mineral slurry was thickening washed to obtain an underflow and an overflow liquid. The underflow was filtered, dried, and subjected to a pelleting and sintering process to obtain an iron ore concentrate with an iron content of 54%, and magnesium oxide was added to the overflow liquid for precipitation reaction. The reaction temperature was controlled at 65°C, and the pH of the solution was 7.0. After 1.5 h of precipitation reaction, the resultant mixture was filtered to obtain a first precipitation filter residue. Then, in a closed reactor, a sodium hydroxide solution was added to the first precipitation filter residue, with the pH value of the reaction solution controlled at 12.5 and the reaction temperature controlled at 140°C. After 1 h of reaction, the resultant mixture was filtered to obtain a second precipitation filter residue and a filtrate. The filtrate was subjected to a precipitation treatment by a carbonation decomposition process, and the resultant mixture was filtered to obtain an aluminium hydroxide precipitate. The second precipitation filter residue was mixed with a sulfuric acid solutoin, with the pH of the reaction solution controlled at 2.0 and the reaction temperature controlled at 80°C. After 1.5 h of reaction, the resultant mixture was filtered to obtain a solution of nickel, cobalt, manganese and scandium sulfates. Then, scandium was subjected to extraction, stripping and crystallization to produce scandium oxalate. The scandium oxalate was calcined and decomposed at 650°C to obtain Sc 2 03 with a content of 98%, which was sold as a commodity. A liquid obtained after extracting scandium was subjected to fractional extraction of manganese/cobalt/nickel and crystallization to obtain a nickel sulfate solution, a cobalt sulfate solution, a manganese sulfate solution and a scandium salt soltuion. Each of the solutions was subjected to an evaporation concentration treatment respectively to obain products of nickel, cobalt and manganese. The first precipitation filtrate was subjected to evaporation concentration to obtain a magnesium nitrate crystal, which was heated and melted and then directed into a decomposing furnace at a temperature of 450°C. The magnesium nitrate was rapidly decomposed into a nitrogen oxide gas, steam, magnesium oxide and oxygen in the decomposing furnace. Then, a high purity active magnesium oxide with a content greater than 92.3% was obtained after dedusting, and 80% of the gas obtained after dedusting was heated by a burner, and entered into the decomposing furnace again for heating and decomposing magnesium nitrate. The other portion of the gas was subjected to deep dedusting, and then cooled to 40°C to obtain a condensed nitric acid at a concentration of 33%. The remaining gas was pressurized to 4.1 MPa by a nitroge oxide compressor, and then directed to an absorber. Meanwhile, the condensed acid obtained was pumped to respective trays of the absorber, finally obtaining a regenerated nitric acid at a concentration of 48% at the bottom, and a tail gas obtained after absorption was discharged after being treated to meet the discharge requirement. Example 2 A raw laterite-nickel ore containing 0.87% of nickel, 0.085% of cobalt, 49% of iron, 1.9% of aluminum, 0.9% of manganese, 1.3% of magnesium, and 66 g/t of scandium was crushed and finely ground to obtain mineral powders as a raw material for subsequent use. The mineral powders, nitric acid, and water were well stirred and mixed at a liquid-solid ratio of 1:2 g/mL and an initial acid concentration of 150 g/L in a slurrying tank to prepare a mineral slurry, and then the mineral slurry was pumped into a nitric acid autoclave for leaching. The leaching was performed at a leaching temperature of 180°C for a leaching period of 2 h at a stirring speed of 180 rpm. After the reaction, magnesium oxide was added into the mineral slurry to pre-neutralize it to adjust the pH to 2.5, and then the mineral slurry was thickening washed to obtain an underflow and an overflow liquid. The underflow was filtered, dried, and subjected to a pelleting and sintering process to obtain an iron ore concentrate with an iron content of 59%. Magnesium oxide was added to the overflow liquid for precipitation reaction, with the reaction temperature controlled at 80°C and the pH value of the solution controlled at 8.0. After 1 h of precipitation reaction, the resultant mixture was filtered to obtain a first precipitation filter residue. Then, in a closed reactor, a sodium hydroxide solution was added to the first precipitation filter residue, with the pH value of the reaction solution controlled at 13.0 and the reaction temperature controlled at 160°C. After 3 h of reaction, the resultant mixture was filtered to obtain a second precipitation filter residue and a filtrate. The filtrate was subjected to a precipitation treatment by a carbonation decomposition process, and the resultant mixture was filtered to obtain an aluminium hydroxide precipitate. The second precipitation filter residue was mixed with a sulfuric acid solutoin, with the pH of the reaction solution controlled at 1.0 and the reaction temperature controlled at 40°C. After 2.0 h of reaction, the resultant mixture was filtered to obtain a solution of nickel, cobalt, manganese and scandium sulfates. Then, scandium was subjected to extraction and crystallization to produce scandium nitrate. The scandium nitrate was calcined and decomposed at 500 0C to obtain Sc203 with a content of 97%, which was sold as a commodity. A liquid obtained after extracting scandium was subjected to fractional extraction of manganese/cobalt/nickel and crystallization to obtain a nickel sulfate solution, a cobalt sulfate solution, a manganese sulfate solution and a scandium salt soltuion. Each of the solutions was subjected to an evaporation concentration treatment respectively to obain products of nickel, cobalt and manganese. The first precipitation filtrate was subjected to evaporation concentration to obtain a magnesium nitrate crystal, which was heated and melted and then directed into a decomposing furnace at a temperature of 5000 C. The magnesium nitrate was rapidly decomposed into a nitrogen oxide gas, steam, magnesium oxide and oxygen in the decomposing furnace. Then, a high purity active magnesium oxide with a content greater than 94.3% was obtained after dedusting, and 60% of the gas obtained after dedusting was heated by a burner, and entered into the decomposing furnace again for heating and decomposing magnesium nitrate. The other portion of the gas was subjected to deep dedusting, and then cooled to 100°C to obtain a condensed nitric acid at a concentration of 27%. The remaining gas was pressurized to 4.2 MPa by a nitroge oxide compressor, and then directed to an absorber. Meanwhile, the condensed acid obtained was pumped to respective trays of the absorber, finally obtaining a regenerated nitric acid at a concentration of 49% at the bottom, and a tail gas obtained after absorption was discharged after being treated to meet the discharge requirement. Example 3 A raw laterite-nickel ore containing 1.0% of nickel, 0.11% of cobalt, % of iron, 2.7% of aluminum, 1.5% of manganese, 2.7% of magnesium, and 85g/t of scandium was crushed and finely ground to obtain mineral powders as a raw material for subsequent use. The mineral powders, nitric acid, and water were well stirred and mixed at a liquid-solid ratio of 1:3 g/mL and an initial acid concentration of 180 g/L in a slurrying tank to prepare a mineral slurry, and then the mineral slurry was pumped into a nitric acid autoclave for leaching. The leaching was performed at a leaching temperature of 170°C for a leaching period of 3 h at a stirring speed of 190 rpm. After the reaction, magnesium oxide was added into the mineral slurry to pre-neutralize it to adjust the pH to 3.0, and then the mineral slurry was thickening washed to obtain an underflow and an overflow liquid. The underflow was filtered, dried, and subjected to a pelleting and sintering process to obtain an iron ore concentrate with an iron content of 56%. Magnesium oxide was added to the overflow liquid for precipitation reaction, with the reaction temperature controlled at 70°C and the pH value of the solution controlled at 7.5. After 3.0 h of precipitation reaction, the resultant mixture was filtered to obtain a first precipitation filter residue. Then, in a closed reactor, a sodium hydroxide solution was added to the first precipitation filter residue, with the pH value of the reaction solution controlled at 14.0 and the reaction temperature controlled at 180°C. After 2 h of reaction, the resultant mixture was filtered to obtain a second precipitation filter residue and a filtrate. The filtrate was subjected to a precipitation treatment by a carbonation decomposition process, and the resultant mixture was filtered to obtain an aluminium hydroxide precipitate. The second precipitation filter residue was mixed with a sulfuric acid solutoin, with the pH of the reaction solution controlled at 0.5 and the reaction temperature controlled at 60°C. After 2.5 h of reaction, the resultant mixture was filtered to obtain a solution of nickel, cobalt, manganese and scandium sulfates. Then, scandium was subjected to extraction and crystallization to produce scandium chloride. The scandium chloride was calcined and decomposed at 800°C to obtain Sc 2 03 with a content of 99%, which was sold as a commodity. A liquid obtained after extracting scandium was subjected to fractional extraction of manganese/cobalt/nickel and crystallization to obtain a nickel sulfate solution, a cobalt sulfate solution, a manganese sulfate solution and a scandium salt soltuion. Each of the solutions was subjected to an evaporation concentration treatment respectively to obain products of nickel, cobalt and manganese. The first precipitation filtrate was subjected to evaporation concentration to obtain a magnesium nitrate crystal, which was heated and melted and then directed into a decomposing furnace at a temperature of 600°C. The magnesium nitrate was rapidly decomposed into a nitrogen oxide gas, steam, magnesium oxide and oxygen in the decomposing furnace. Then, a high purity active magnesium oxide with a content greater than 98.2% was obtained after dedusting, and 50% of the gas obtained after dedusting was heated by a burner, and entered into the decomposing furnace again for heating and decomposing magnesium nitrate. The other portion of the gas was subjected to deep dedusting, and then cooled to 80°C to obtain a condensed nitric acid at a concentration of 30%. The remaining gas was pressurized to 4.5 MPa by a nitroge oxide compressor, and then directed to an absorber. Meanwhile, the condensed acid obtained was pumped to respective trays of the absorber, finally obtaining a regenerated nitric acid at a concentration of 53% at the bottom, and a tail gas obtained after absorption was discharged after being treated to meet the discharge requirement. Example 4 A raw laterite-nickel ore containing 1.5% of nickel, 0.14% of cobalt, 43% of iron, 3.5% of aluminum, 2.1% of manganese, 3.6% of magnesium, and 91 g/t of scandium was crushed and finely ground to obtain mineral powders as a raw material for subsequent use. The mineral powders, nitric acid, and water were well stirred and mixed at a liquid-solid ratio of 1:4 g/mL and an initial acid concentration of 200 g/L in a slurrying tank to prepare a mineral slurry, and then the mineral slurry was pumped into a nitric acid autoclave for leaching. The leaching was performed at a leaching temperature of 190°C for a leaching period of 2.5 h at a stirring speed of 200 rpm. After the reaction, magnesium oxide was added into the mineral slurry to pre-neutralize it to adjust the pH to 2.5, and then the mineral slurry was thickening washed to obtain an underflow and an overflow liquid. The underflow was filtered, dried, and subjected to a pelleting and sintering process to obtain an iron ore concentrate with an iron content of 53%. Magnesium oxide was added to the overflow liquid for precipitation reaction, with the reaction temperature controlled at 55°C and the pH value of the solution controlled at 9.0. After 2.5 h of precipitation reaction, the resultant mixture was filtered to obtain a first precipitation filter residue. Then, in a closed reactor, a sodium hydroxide solution was added to the first precipitation filter residue, with the pH value of the reaction solution controlled at 14.0 and the reaction temperature controlled at 170°C. After 1 h of reaction, the resultant mixture was filtered to obtain a second precipitation filter residue and a filtrate. The filtrate was subjected to a precipitation treatment by a carbonation decomposition process, and the resultant mixture was filtered to obtain an aluminium hydroxide precipitate. The second precipitation filter residue was mixed with a sulfuric acid solutoin, with the pH of the reaction solution controlled at 3.0 and the reaction temperature controlled at 70°C. After 3 h of reaction, the resultant mixture was filtered to obtain a solution of nickel, cobalt, manganese and scandium sulfates. Then, scandium was subjected to extraction and crystallization to produce scandium oxalate. The scandium oxalate was calcined and decomposed at 650 0C to obtain Sc203 with a content of 99%, which was sold as a commodity. A liquid obtained after extracting scandium was subjected to fractional extraction of manganese/cobalt/nickel and crystallization to obtain a nickel sulfate solution, a cobalt sulfate solution, a manganese sulfate solution and a scandium salt soltuion. Each of the solutions was subjected to an evaporation concentration treatment respectively to obain products of nickel, cobalt and manganese. The first precipitation filtrate was subjected to evaporation concentration to obtain a magnesium nitrate crystal, which was heated and melted and then directed into a decomposing furnace at a temperature of 7000 C. The magnesium nitrate was rapidly decomposed into a nitrogen oxide gas, steam, magnesium oxide and oxygen in the decomposing furnace. Then, a high purity active magnesium oxide with a content greater than 98.8% was obtained after dedusting, and 40% of the gas obtained after dedusting was heated by a burner, and entered into the decomposing furnace again for heating and decomposing magnesium nitrate. The other portion of the gas was subjected to deep dedusting, and then cooled to 50 0C to obtain a condensed nitric acid at a concentration of 31.9%. The remaining gas was pressurized to 4.7 MPa by a nitroge oxide compressor, and then directed to an absorber. Meanwhile, the condensed acid obtained was pumped to respective trays of the absorber, finally obtaining a regenerated nitric acid at a concentration of 55% at the bottom, and a tail gas obtained after absorption was discharged after being treated to meet the discharge requirement. Example 5

A raw laterite-nickel ore containing 1.8% of nickel, 0.19% of cobalt, 38% of iron, 4.3% of aluminum, 2.7% of manganese, 4.5% of magnesium, and 119 g/t of scandium was crushed and finely ground to obtain mineral powders as a raw material for subsequent use. The mineral powders, nitric acid, and water were well stirred and mixed at a liquid-solid ratio of 1:0.5 g/mL and an initial acid concentration of 130 g/L in a slurrying tank to prepare a mineral slurry, and then the mineral slurry was pumped into a nitric acid autoclave for leaching. The leaching was performed at a leaching temperature of 220°C for a leaching period of 0.5 h at a stirring speed of 200 rpm. After the reaction, magnesium oxide was added into the mineral slurry to pre-neutralize it to adjust the pH to 3.5, and then the mineral slurry was thickening washed to obtain an underflow and an overflow liquid. The underflow was filtered, dried, and subjected to a pelleting and sintering process to obtain an iron ore concentrate with an iron content of 50%. Magnesium oxide was added to the overflow liquid for precipitation reaction, with the reaction temperature controlled at 90°C and the pH value of the solution controlled at 10.0. After 1.0 h of precipitation reaction, the resultant mixture was filtered to obtain a first precipitation filter residue. Then, in a closed reactor, a sodium hydroxide solution was added to the first precipitation filter residue, with the pH value of the reaction solution controlled at 12.5 and the reaction temperature controlled at 200°C. After 2 h of reaction, the resultant mixture was filtered to obtain a second precipitation filter residue and a filtrate. The filtrate was subjected to a precipitation treatment by a carbonation decomposition process, and the resultant mixture was filtered to obtain an aluminium hydroxide precipitate. The second precipitation filter residue was mixed with a sulfuric acid solutoin, with the pH of the reaction solution controlled at 0.5 and the reaction temperature controlled at 65°C. After 3 h of reaction, the resultant mixture was filtered to obtain a solution of nickel, cobalt, manganese and scandium sulfates. Then, scandium was subjected to extraction and crystallization to produce scandium oxalate. The scandium oxalate was calcined and decomposed at 700°C to obtainSc 203with a content of 99%, which was sold as a commodity. A liquid obtained after extracting scandium was subjected to fractional extraction of manganese/cobalt/nickel and crystallization to obtain a nickel sulfate solution, a cobalt sulfate solution, a manganese sulfate solution and a scandium salt soltuion. Each of the solutions was subjected to an evaporation concentration treatment respectively to obain products of nickel, cobalt and manganese. The first precipitation filtrate was subjected to evaporation concentration to obtain a magnesium nitrate crystal, which was heated and melted and then directed into a decomposing furnace at a temperature of 850°C. The magnesium nitrate was rapidly decomposed into a nitrogen oxide gas, steam, magnesium oxide and oxygen in the decomposing furnace. Then, a high purity active magnesium oxide with a content greater than 99% was obtained after dedusting, and 20% of the gas obtained after dedusting was heated by a burner, and entered into the decomposing furnace again for heating and decomposing magnesium nitrate. The other portion of the gas was subjected to deep dedusting, and then cooled to 60°C to obtain a condensed nitric acid at a concentration of 31%. The remaining gas was pressurized to 5.0 MPa by a nitroge oxide compressor, and then directed to an absorber. Meanwhile, the condensed acid obtained was pumped to respective trays of the absorber, finally obtaining a regenerated nitric acid at a concentration of 56% at the bottom, and a tail gas obtained after absorption was discharged after being treated to meet the discharge requirement. The foregoings are only preferred particular embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Variations or replacement, which can be readily envisaged by those skilled in the art within the technical scope as disclosed in the present invention, should fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be defined by the protection scopes of the appended claims.

Claims (3)

Claims

1. A method for recovering valuable metals from a laterite-nickel ore and regenerating and recycling two mediums of acid and alkaline, comprising steps of: (1) crushing and finely grinding a raw laterite-nickel ore to obtain mineral powders, and mixing and well stirring the mineral powders and nitric acid to prepare a mineral slurry; the laterite-nickel ore being a limonitic high iron and low nickel ore with a chemical composition of: 0.5-2.0 mass% of Ni; 0.05-0.20 mass% of Co; 35-55 mass% of Fe; 0.5-5.0 mass% of Al; 0.1-3.0 mass% of Mn; 0.50-5.0 mass% of Mg; and -130 g/t of Sc; the nitric acid is at a concentration of 180-200 g/L, and a solid liquid ratio of a mixture of the mineral powders and the nitric acid is 1:3-1:4 g/ml; (2) pumping the mineral slurry into an autoclave for a leaching reaction, magnesium oxide being added to the mineral slurry after the leaching reaction for pre-neutralization to adjust the pH value of the mineral slurry to 2.5-3, and then subjecting the mineral slurry to a multistage thickening washing to obtain an underflow and an overflow liquid; the leaching reaction being performed at a leaching temperature of 170-220°C for a leaching period of 2.5-3 h; the autoclave being equipped with a stirrer which stirs the mineral slurry during leaching at a stirring speed of 190-200 rpm; (3) subjecting the underflow to filtering, drying and pellet sintering to obtain an iron ore concentrate, and subjecting the overflow liquid to a precipitation reaction by adjusting a pH value of the overflow liquid, such that aluminum, nickel, cobalt, manganese, scandium and a minor amount of iron in an acid leaching solution are completely precipitated and separated from a magnesium nitrate solution after the reaction, and filtering out the aluminum, nickel, cobalt, manganese, scandium and a minor amount of iron to obtain a first precipitation filter residue; magnesium oxide being added to the overflow liquid to adjust the pH value of the overflow liquid to 7.5-9.0; and the precipitation reaction is performed at a reaction temperature of 55-70°C for a reaction period of 2.5-3 h. (4) adding an alkaline to the first precipitation filter residue to convert aluminium hydroxide in the filter residue to an aluminate ion which is then dissolved in an alkaline solution, filtering the resultant mixture to obtain a second precipitation filter residue, and adding a carbon dioxide or aluminium hydroxide seed crystal in a filtrate obtained after filtering for precipitation to obtain a product of aluminium hydroxide; adding the alkaline to the first precipitation filter residue for dissolving being performed at a reaction temperature of 140-200°C for a reaction period of 1-4 h at a pH value in a range of 12.5-14.0; the alkaline used comprising any one of sodium hydroxide and potassium hydroxide or a combination thereof; and the carbon dioxide or aluminium hydroxide seed crystal being added to the filtrate obtained after filtering out the second precipitation filter residue to obtain a product of aluminium hydroxide; (5) dissolving the second precipitation filter residue with sulfuric acid, then extracting scandium, stripping the scandium, and crystalizing the scandium to produce a scandium slat, using a liquid obtained after extracting scandium for preparing a nickel-cobalt-manganese ternary material, or subjecting the liquid to fractional extraction, stripping and crystallization to produce products of nickel, cobalt, and manganese; dissolving the second precipitation filter residue with sulfuric acid being perfomred at a reaction temperature of 60-70°C for a reaction period of 1.0-2.5 h at a pH in a range of 0.5-3.5; and the scandium salt comprising any one of scandium oxalate, scandium nitrate and scandium chloride; pyrolyzing the scandium salt produced at a heating temperature of 650°C-800°C to obtain scandium oxide, and the pyrolyzing being calcinationpyrolysis; (6) subjecting a first precipitation filtrate to evaporation concentration to obtain a magnesium nitrate crystal, which is then heated and melted and sent to a decomposing furnace for pyrolysis to form a high temperature dust gas; the decomposing temperature in the decomposing furnace being between 600°C and 700°C; (7) separating magnesium oxide powders from the high temperature dust gas through a dust collecting system, and returning the magnesium oxide produced to the first precipitation procedure; heating a portion of NOx gas obtained after dust collecting through a burner; recycling the heated NOx gas to the burner for pyrolyzing magnesium nitrate; sending the other portion of NOx to a nitric acid regeneration system, and subjecting the NOx to tail gas heat exchange, deep dedusting and twice cooling condensation to obtain a dilute nitric acid, pumping the condensed acid to an absorber, pressurizing and densifying a gas which is not condensed and absorbed through a nitrogen oxide compressor, sending the gas to the absorber to prepare nitric acid, and returning the nitric acid produced to the leaching procedure.

2. The method according to claim 1, characterized in that, in Step (6), the pyrolysis in the decomposing furnace comprises any one of boiling pyrolysis, calcination pyrolysis and spray pyrolysis; and the high temperature dust gas comprises magnesium oxide, steam, NOx and oxygen.

3. The method according to claim 1, characterized in that, in Step (7), 20-95% of the NOx gas obtained after dust collecting is heated through the burner, and recycled to the decomposing furnace for pyrolyzing magnesium nitrate; the NOx enters into the nitric acid regeneration system and has its temperature decreased to 120°C or lower when it arrives at a cooling system to obtain a condensed dilute nitric acid, and the condensed dilute nitric acid is at a concentration of 20-35%; the NO, which is not condensed and absorbed is pressurzied to 4.0 MPa-5.0 MPa, and sent to the absorber to be absorbed to prepare nitric acid, during which the previous condensed dilute nitric acid is used as an absorbent, and a tail gas obtained after absorption is discharged after being treated to meet the discharge requirement.

ore laterite-nickel Limonitic grinding finely and Crushing powders Mineral leaching Pressure slurry Leaching Pre-neutralizing Underflow

Thickening Iron ore Drying/sintering hydroxide/ Sodium concentrate hydroxide potassium Overflow CO2/AL(OH)3

aluminum, of Precipitates nickel, aluminum, Precipitating Leaching Aluminum

leaching Alkaline cobalt nickel, scandium, scandium and manganese cobalt, Adjusting pH

solution hydroxide

manganese and and manganese cobalt, Nickel, solution nitrate Magnesium material scandium-enriched Nitric acid acid Sulfuric crystallization and Evaporation leaching Acid an in Absorbing nitrate Magnesium absorber and manganese cobalt, Nickel, sulfates scandium a in Pyrolyzing and Pressurizing furnace decomposing densifying scandium/ Extracting Scandium

T Sc2O3

Pyrolyzing

stripping/crystallization MgO salt

NO collecting Dust x T and Dedusting Condensed and cobalt nickel, of Solution acid nitric NO NOx of portion a (Heating cooling sulfates manganese ) it recycling and burner a in extracting Fractional manganese/cobalt/nickel sulfate/cobalt nickel of Solutions sulfate sulfate/manganese Stripping/crystallization sulfate/cobalt nickel of Products sulfate sulfate/manganese