A METHOD OF RECOVERING CALCIUM AND SULPHUR COMPOUNDS FROM A METALLURGICAL WASTE MATERIAL

Abstract: A pulverulent waste material containing CaO and CaS is suspended in water (4), and H<u2>uS is subsequently added (9), resulting in CaO and CaS being dissolved, forming Ca(SH)<u2>u. H<u2>uS is driven off in a first step (11) in a quantity required for said dissolution. In a second step (26) H<u2>uS is driven off while Ca precipitates as Ca(OH)<u2>u or CaCO<u3>u, which are removed by filtration (36). The excess quantity of H<u2>uS is withdrawn (32) for some suitable purpose.

Description: TITLE OF INVENTION: A METHOD OF RECOVERING CALCIUM AND SULPHUR COMPOUNDS FROM A METALLURGICAL WASTE MATERIAL. TECHNICAL FIELD: The invention relates to a method of recovering calcium and sulphur compounds from a metallurgical waste material. More specifically, the invention relates to a method of recovering calcium hydroxide or calcium carbo¬ nate, or both, and hydrogen sulphide from the waste mate- rial which is produced when sulphur is removed from a metallurgical material by means of lime. The waste material may originate, for example, from the removal of sulphur from raw iron by means of pulverulent lime, or from the prereduction of iron ore concentrate in the presence of lime. BACKGROUND ART: A metallurgical waste material of the type concern¬ ed may be produced in the reduction of iron ore concen¬ trate in a fluidized bed. The reducing agent added to the fluidized bed is fine-grained lignite coal, mineral coal, anthracite coal, or the like. In order to bind the sul¬ phur added with the reducing agent, a fine-grined CaO- material is added, such as burnt lime, burnt dolomite, limestone or dolomite. The product withdrawn from the fluidized bed is cooled and subjected to a magnetic se¬ paration resulting in two portions, viz. a first portion substantially consisting of Fe, FeO and coke, and a second portion substantially consisting of coke, coke ash, gangue, CaO and CaS. This second portion is a useful starting material for the process of the invention. A reduction process of this type is disclosed in Swedish patent No. 7502369-7, published under No. 388 875, and the equivalent U.K. patent No. 1 508 273. OMPI /., IPO _ DISCLOSURE OF INVENTION: The method of this invention consists of the com¬ bination of these operations: 1. A selected flow of the pulverulent waste mate al is suspended under agitation in an aqueous phase. 2. Gaseous H-S is injected into the suspension resulting from operation 1, said H~S having been produc in operation 4 described below. The flow of H S is reg lated so that the partial pressure of H 2 S in the gaseous phase above the suspension is at least 0.1 bar, suitabl 0.2-5 bar, and preferably 0.5-1.5 bar. The temperature the suspension may vary, but is preferably 20-90°C. The chemical reaction taking place in this operation is as follows: (l-x)CaO + xCaS + (2-x)H 2 S = Ca(SH) 2 + (l-x)H 2 0 (1 in which 0 < x < 1. The formula means that CaO and CaS are dissolved, forming Ca(SH) 2 . If this reaction is to proceed at a sufficiently high speed it is necessary that the solut¬ ion contains free H 2 S, which means that there shall be some partial pressure of H 2 S in the gaseous phase above the solution. If this partial pressure is at least 0.1 bar, the reaction speed is satisfactory for practical use. The reaction speed increases with the partial pressure of the H 2 S. Therefore, it is useful to maintai a partial pressure of 0.2-5 bar, preferably 0.5-1.5 bar. It appears that there is no use in maintaining a still higher partial.ipressure of H 2 S. 3_^_ Insoluble material is separated from the solut ion produced in operation 2, for example by sedimentat¬ ion or filtering. The insoluble material is disposed of. 4. H 2 S is driven off from the solution produced i operation 3. The flow of H 2 S shall be selected to cover the demand of H 2 S in operation 2. The H 2 S can be driven off, for example by exposing the solution to vacuum or .-g ( ( by blowing steam into the s olution . The best way , however . of driving off H 2 S is to blow C0 2 into the s olution , and to s elect the flow of CO- s o that the release d H 2 S covers the demand of H 2 S in operation 2 . The chemical reaction taking place in this operation is : Ca (SH) 2 + -- - C0 2 + ϊ - H 2 0 = (2 -x.) H 2 S + + -^ CaC0 3 + Ca (SH) 2 It can be seen from formula (2) that the flow of C0 2 has been limited so as to produce only so much H 2 S as is required in operation 2, viz. (2-x)H 2 S, vide formula (1). This means that only part of the Ca(SH) 2 in the solution coming from operation 2 is decomposed and transformed into CaCO,. 5. The remaining H 2 S in the suspension coming from operation 4 is driven off. This can be done by means of vacuum or steam. The result is that Ca(0H) 2 precipitates, and a gaseous mixture of H 2 S and water vapour leaves the suspension. The water vapour is removed by cooling the gaseous mixture, and the H 2 S is withdrawn for further processing. It may, for example, be converted by known methods into elementary sulphur, S0 2 , H 2 S0,. It is preferred, however, to drive off the H 2 S by means of C0 2 . The result is that CaC0 3 precipitates, and a gaseous mixture of H 2 S and C0 ? leaves the suspension. The flow of C0 2 is controlled so that said gaseous mixture contains at least 5 per cent by volume of C0 2 , suitably 5-50 and preferably 10-30 per cent by volume. The chemical reaction taking place in this operation is: ^CaC0 3 + Ca(SH) 2 + (|+Δ)C0 2 + |H 2 0 = .*-- = CaC0 3 + xH 2 S + ΔC0 2 It can be seen from formula (3) that the flow of C0 2 is controlled so that the released gas contains C0 2 . The C0 2 flow is preferably selected so that Δ > 0.05x. -m ETlj- OMPI_ 6. The Ca(OH) 2 or the CaCO^ produced in operat¬ ions 4 and 5 is separated from the aqueous solution by sedimentation, filtering or in any other known way. 7. The aqueous solution from operation 6 may be used for suspending pulverulent waste material in operation 1. BEST MODE OF CARRYING OUT THE INVENTION WITH REFERENCE TO THE DRAWING: A selected flow of a pulverulent material is fed from a feed hopper 1 via a weighing conveyor 2 to a container 4 containing a mixer 3a driven by a motor 3b. The material contains the following constituents, the contents being given as per cent by weight: Coke Ashes Gangue CaO CaS 29.8 19.7 34.5 9.0 7.0 A selected flow of water is supplied to the con¬ tainer 4 from a return water container 6 via a conduit 45 provided with a flow control valve 5a operated by a flow sensor 5b. The pulverulent material is suspended in the wa er in the container 4, and the suspension is pumped through a conduit 47 by a pump 7 to a first reaction tank 9 containing an agitator 8a driven by a motor 8b. A selected flow of water is supplied to the reaction tank 9 from the return water container via said conduit 45 and a conduit 46 provided with a con¬ trol valve 10a operated by a flow sensor 10b. Gaseous H 2 S from a second reaction tank 11 is supplied in a controlled flow into the bottom portion of the first reaction tank 9 via a conduit 49 and a distribution member 12. Excess H 2 S leaves the tank 9 through a conduit 32. The desired partial pressure of H 2 S in the gas-filled space of the tank 9 is mantained by means of a control valve 13a in said conduit 32. The control valve 13a is operated by a pressure sensor 13b. O The suspension formed in the tank 9 contains coke, ashes and gangue suspended in a solution of Ca(SH) 2 . This suspension is conveyed to hydrocyclone separators 14. The liquid from these separators is passed through a conduit 50 and a pump 20 to the second reaction tank 11. The con¬ duit 50 contains a control valve 15a operated by a liquid level sensor 15b in the first reaction tank 9 so as to maintain a constant liquid level in said tank 9. The flows of reject material from the separators 14 are pumped by sludge pumps 16 to a filter 17a containing a vacuum cylinder 17b. In this filter the content of solids is separated and washed. The filter cake, containing coke, ashes and ga gue, is removed. The filtrate is conveyed to a container 18 and is pumped from this container 18 via a conduit 48 to the first reaction tank 9. The con¬ duit 48 contains a flow control valve 19a operated by a liquid level sensor 19b in the container 18. The/liquid from the separator 14 is a solution of CaS and CaSH. It is conveyed by the pump 20 into the second reaction tank 11. The liquid flows down through a plurality of perforated platforms 21 to the bottom portion of the tank, which contains an agitator 22a, driven by a motor 22b and a gas distribution member 23. A selected flow of C0 2 is blown into the tank 11 via conduits 42, 43 containing a flow control valve 24a operated by a flow sensor 24b. The conduit 43 is connect¬ ed to said gas distribution member 23. The flow of C0 2 is controlled so that the resulting flow of H 2 S, which is passed to the tank 9, is adequate for dissolving the CaO + CaS supplied to the tank 9, vide formulas 1 + 2. The pump 20 produces in the tank 11 a pressure sufficiently high for the H 2 S to be pressed over into the tank 9. A suspension of CaCO ? in a solution of Ca(SH) 2 is formed in the tank 11. This suspension is conveyed to a third reaction tank 26 via a conduit 51 containing a flow control valve 25a operated by a liquid level sensor 25b in the tank 11. The upper portion of the third reaction tank 26 contains a plurality of perforated platforms 27. The su pension flows down through said platforms, in counter- -current flow to a gaseous mixture coming from the lowe portion of the tank. The suspension is collected in the lower portion of the tank, where an agitator 28a driven by -a motor 28b and a gas distribution member 29 are pro vided. A selected flow of C0 2 is supplied to the tank 26 via a conduit 44 and said gas distribution member 29. The conduit 44 contains a flow control valve 30a operat by a flow sensor 30b.The flow of C0 2 is controlled so that the resulting H 2 S gas leaving the tank 26 via a pressure control valve 31a operated by a pressure senso 31b contains > 5. C0 2 , suitably 5-50. C0 2 , and preferab 10-30% C0 2 . This gas is withdrawn from the plant throug a conduit 32 which also receives the H 2 S leaving the tank 9. The gas may be conveyed, for example, to a Clau plant in which the sulphur content of the gas is con- verted into elementary S. A suspension of CaCO, in water is formed in the tank 26. This suspension is conveyed to the return wate container 6 via a conduit 52 and hydrocyclone separator 34. The conduit 52 contains a flow control valve 33a operated by a liquid level sensor 33b in the tank 26. The reject material from the separators 34 is pum ed by sludge pumps 35 to a vacuum filter 36, in which t solids is separated and washed. The filter cake, contai ing CaCO,, is removed, and the filtrate is collected in container 37 from which it is pumped by a pump 39 via a conduit 54 to the return water container 6. The conduit 54 contains a flow control valve 38a operated by a liquid level sensor 38b in the container 37. The plant as illustrated looses water via the fil ter cakes from the filters 17 and 36. Water to compen¬ sate for this loss is supplied by the addition of selected flows of washing water to the filters and fresh water to the return water cont ainer 6 through a conduit 40. From s aid container 6 water is conveyed by a pump 41 through the conduit 45 to the suspens ion container 4 and the firs t reaction tank 9 .

Claims: CLAIMS : 1. A method of recovering calcium and sulphur compounds from a material containing CaO and CaS , characterized in the combination of the following oper ions : 1.1 Suspending a powder of the material in an aqueous phase ", 1.2 Inj ecting a flow of H 2 S into said suspens ion w-hile controlling the flow of H 2 S to maintain a partial pressure of H 2 S in the gaseous phase above the suspensi of at least 0.1 bar , suitably 0.2-5 bar , and preferably 0.5-1.5 bar , CaO and CaS being dissolved while forming Ca(SH) 2 ; 1.3 Separating insoluble material from the H 2 S- -containing solution of Ca(SH) 2 produced. in operation 1 1.4 Driving off H 2 S from the H 2 S-containing solut ion of Ca(SH) 2 produced in operation 1.3 , to produce a flow of H 2 S selected to cover the demand of gaseous H 2 S in operation 1.2 ; 1. 5 Driving off the residual H 2 S from the solutio produced in operation 1.4 ; 1.6 Separating the precipitated Ca(0H) 2 or CaCO, , or both , produced in operations 1.4 and 1.5 from the aqueous phase ; 1. 7 Recycling the aqueous phase from operation 1. to the suspending process in operation 1 .1. 2. A method as claimed in claim 1 , characterize in driving off the H 2 S in operations 1.4 and 1.5 by means of vacuum. 3. A method as claimed in claim 1 , characterize in driving off the H 2 S in operations 1. 4 and 1.5 by - means of steam. 4. A method as claimed in claim 1, characterized in driving off the H-.S in Operations 1.4 and 1.5 by means of C0 2 . 5. A method as claimed in claim 4, characterized in driving off H 2 S in operation 1.4 with C0 2 in a flow selected to produce in the leaving H 2 S a C0 2 content of at least 5 per cent by volume of C0 2 , suitably 5-50 per cent, and preferably 10-30 per cent. WIPO

Inventors: COLLIN P
Applicants: COLLIN P
Application year: 1979
Main classification: C01F11
IPC codes: C01B17, C01F11