WO2010057225A2

WO2010057225A2 - ADDITIVES FOR Cr (VI) REDUCTION IN CEMENT, SLAGS, MORTARS, CONCRETE, WASTE WATER AND MINING INDUSTRY WASTE

Info

Publication number: WO2010057225A2
Application number: PCT/ZA2009/000094
Authority: WO
Inventors: Jean-Bosco Kazirukanyo
Original assignee: Afrisam (South Africa) (Pty) Ltd
Priority date: 2008-11-11
Filing date: 2009-10-28
Publication date: 2010-05-20
Also published as: EP2364281A2; EP2364281A4; WO2010057225A3

Abstract

The invention provides a Cr (VI) or Cr⁶⁺ reduction and/or immobilization additive compositions for use in cement, cement based products, and in slags which composition includes one or more chemical compounds containing the element N in the form of simple or complex anions and/or metallic Zn powder, Zn salts, and/or Zn compounds.

Description

ADDITIVES FOR Cr (Vl) REDUCTION IN CEMENT, SLAGS, MORTARS, CONCRETE, WASTE WATER AND MINING INDUSTRY WASTE

Field of the Invention

The invention relates to additives for Cr (Vl) or Cr⁶⁺ reduction. In particular the invention relates to additives for Cr (Vl) reduction in cement, cement bricks, cement mortars, cement blocks, concrete, cementitious products, slags, mining industry waste and, industrial wastewater.

Background of the Invention

Cr (Vl) is a known carcinogen often present in cement compositions which remains present for years or even decades after the cement has been used in construction of buildings. In many countries the level of Cr (Vl) in cement and cementitious products is legislated and cement producers around the world have considered as to how to reduce the amount of Cr (Vl) in cement either during production thereof or during preparation of cementitious products from the cement.

Thus, for example, US Patent 7,232,483 provides compositions and methods for reducing hexavalent chromium in cementitious compositions involving the use of a liquid additive composition, comprising stannous chloride. Along with the stannous chloride may be used at least one co-additive comprising an antioxidant, oxygen scavenger, or mixture thereof, and/or at least one agent comprising a cement grinding aid, cement quality improver, or mixture thereof. i Another example is US Patent 6,872,247 in which methods and compositions involving hexavalent chromate-reducing agents, particularly hydroxylamine, hydrazine, or their salts or derivatives, for use in cement compositions and cement processing are disclosed.

The present invention provides novel methods and compositions capable of reducing the hexavalent Chromium (Cr⁶⁺) in cement, cement based products, concrete, fly ash, silica fume, waste water and mine residues, slags and particularly ferro - chromium slags.

Summary of the Invention

Thus, according to a first aspect of the invention, there is provided a Cr (Vl) or Cr⁶⁺ reduction additive composition for use in cement, cement based products, slags, and wastewater which compositions includes NaNO₂ alone, ZnSO₄.7H₂O alone or, a combination of both and other chemical compounds.

Chemical compounds containing the element N in the form of a simple or composed anion may be selected from N^", N^2"1 N^3" , (NO₂)^", (NO₂)^2" ,(NO₂)^3" , or the like.

The additive composition when used for cementitious applications may contain from 0.01% to 1% of NaNO₂ by mass of cement. In other applications, the NaNO₂ and ZnSO₄.7H₂O dosage may be increased up to 5% wt. The additives may reduce the levels of hexavalent chromium Cr⁶⁺ to less than 1 ppm, typically below 2 ppm.

The additives that contain NaNO₂ are active in neutral, acidic and alkaline environments (pH=0-14)

The above additives may include one or more anions of the element N, in simple or complex forms.

The additives may include one or more organic salts of Na and Ca, for example, Ca (CH₃COO)₂, andCH₃COO-Na.

The additives may include a combination, in any proportions, of one or more of metallic Zn, metallic Mn, metallic Fe, Metallic Mg, metallic Sn powders with NaNO₂, for example Zn+NaNO₂, Fe+NaNO₂, Mg+NaNO₂₎ Sn+NaNO2.

The additives may include a combination, in any proportions, of any of the above compositions with any type of cement grinding aid, for example, acetic acid or acetates, gluconic acid or gluconates, ethanolamine, di-ethanolamine (DEA), tri-ethanolamine (TEA), tri- Iso-propanolamine (TIPA) or any other amine-based grinding aid.

The additives may include the combination, in any proportions, of any of the above compositions, with any cement set and/or hardening accelerators based on or containing any of the chemical elements of Group IA and Group MA of the Periodic Table of Chemical Elements, for example, Ca (HCOO) ₂, Ca (NO₃)₂, CaCI₂, CaCO₃, Ca₂(NO₂J₂, LiNO₃, Li₂CO₃, NaCI, KCI, Na₂CO₃, BaCI2, Ba(NO₃J₂, and MgCI₂.

The additive may include combinations of any of the above compositions with any other reducing agents, organic or inorganic such as ascorbic acid or salt, oxalic acid or salt, FeSO₄, MnSO₄, SnCI₂, SnSO4 in any crystal log raphic forms, Ca(CH3COO)₂, Mg(CH3COO)₂, Al⁰, Fe⁰, Mg⁰, Mn⁰ and Sn⁰.

The additives may include combinations of any of the above compositions with any concrete admixtures _τ for example, lignosulphonate, polynaphthalene, polymelamine, polycarboxylate, polyacrylic, polyester, retarders, anti-shrinkage, anti-washout, anti- alkali silica reaction agents, viscosity modifying agents, or their combinations.

It is believed that NaNO₂ and ZnSO₄.2H₂0 are more cost-effective and, easier to handle in cement, slag, silica fume, concrete, building materials, in construction, and road & mining industries as they do not require any preliminary granulation or crystallization like the currently used FeSO₄.7H₂0 and MnSO₄.7H₂O reducing agents.

The additives containing NaNO₂ may be safely used for wastewater treatment containing large amounts of Cr⁶⁺ at any pH, and in soils and mining industry waste. It may be used in liquid or powder form, alone or in combination with other reducing agents.

Moreover, it is believed, that the new compositions can be added in the form of aqueous solution which are easier to dispense in cement or concrete making when compared to Sn, Mn or Fe-based agents.

The invention extends to pre-blends, in any proportions, of any of the additive compositions disclosed above, with any cement, slag, limestone powder, silica fume, fly ash, clays, pozzolanas, dry mortar, and/or combinations thereof.

The invention extends to cementitious compositions and products thereof, which include additive compositions as described above, added in any form, whether liquid, powder or crystal form, after, before, or together with the addition of mixing water thereto. The cementitious compositions may be used for production of cement-based bricks, blocks, mortars, or concrete.

The invention extends to the addition of one or more additive compositions described above to clinker before or during its milling process, in liquid or powder form.

NaNO₂ and similar agents have the particular ability of reducing high amount of Cr(VI) e.g. IOOOppm Cr(VI) in water and at any pH.

The mechanism of Cr⁶⁺ reduction by NaNO₂, as currently hypothesized is indicated below. It is believed to proceed according to the Redox equation below; which might be autocatalytic: the amount of the Cr(VI) reduced increases as the original amount of Cr(VI) increases for the same amount of NaNO₂ added.

N³⁺ = N⁵⁺ +2e

Cr⁶⁺ + ^ = Cr³⁺

This reaction could form complex compounds as well.

On the other side, the mechanism of Cr⁶⁺ reduction by Zn powder (Zn⁰), as currently hypothesized is indicated below. In case of metallic Zn, it is believed to proceed according to the Redox equation below;

Zn° - 2e= Zn²⁺ Cr⁶⁺ + 3e = 2Cr³⁺ or,

Zn⁰ + Cr⁶⁺ + 2e = Zn²⁺ + 2Cr³⁺.

Cr³⁺ containing products are insoluble in water and are not carcinogenic. It is probable that water soluble Zn salts form insoluble complex compounds in presence of Cr⁶⁺ at alkaline pH.

The potentially new complexes might not release Cr⁶⁺ back in the original products as effect of age and/or temperature like the commonly used Iron sulfate.

The additives prevented oxidation back to Cr⁶⁺ in the treated cements for 9 weeks at 40⁰C.

The additive may include Zn powder and organic salts of Zn, for example, Zn (CH₃COO)₂..

Description of Embodiments of the Invention

The invention is illustrated, by way of example only, with reference to the laboratory experiments and results which follow, which are not intended to limit the scope of the invention.

Example 1: Use of NaNO₂

Laboratory findings

I. Cr(VI) reduction in Cement

Figure 1 shows the amount in ppm of Cr⁶⁺ reduced in Ordinary Portland cement (CEM I) samples with different Cr⁶⁺ contents when NaNO₂ is added to the cement. Reduction in CEM I containing 10ppm Cr(VI)

Reduction in CEM I 10 containing 20ppm Cr(V!)

Reduction in CEM I containing 30ppm Cr(VI)

0.05 0.1 0.15 0.2

Amount of NaN 02 (%wt cement)

Figure 1. Amount of Cr⁶⁺ reduced in Ordinary Portland cement (CEM I) samples containing different amounts of Cr&

Figure 2 shows the ppm, rate of Cr⁶⁺ reduction in the Ordinary Portland cement (CEM I) samples containing different amounts of Cr⁶⁺ when NaNO₂ is added to the cement. In the Figure, the first bar of each set shows the reduction in CEM I containing 10 ppm Cr(VI), the second bar shows the reduction in CEM I containing 20 ppm Cr(VI), and the third bar shows the reduction in CEM I containing 30 ppm Cr(VI).

π Reduction in CEM I containing 10ppm Cr(VI)

■ Reduction in CEM I containing 20ppm Cr(VI)

Reduction in CEM I containing 30ppm Cr (Vl)

0 0.05 0.075 0.1 0.15 0.2 Amount of NaNO2 (Y₀Wt cement}

Figure 2. Rate Of Cr⁶⁺ reduction in Ordinary Portland cement (CEM I) samples containing different amounts of Cr&

II. Effect of NaNO₂ on cement and concrete properties

Figure 3 shows the effect of NaNO₂ on Ordinary Portland cement strength development when NaNO₂ is added to the cement. In the Figure, the first bar of each set shows a reference CEM I, the second bar shows CEM I containing 0.05 wt% NaNO₂, the third bar shows CEM I containing 0.1 wt% NaNO₂, and the fourth bar shows CEM I containing 0.2 wt% NaNO₂.

60.0 (_tum_pm_rrc_ree s _i 51.0 52.1

2

1-d 2-d 7-d 28-d

Age (days)

Fig.3. Effect Of NaNO₂ on Ordinary Portland cement strengths development

Figure 4 shows the effect of NaNO₂ on concrete slump retention

130

101

0 30 60 90 120 150

Slump Retention (minutes)

Fig.4. Effect OfNaNO₂ on concrete slump retention development (the dosage is related to the amount of cementitious materials) III. Effect of the different modes of addition of NaNO₂ to cement on Cr(VI) reduction

Figure 5 shows the effect of the mode of addition of NaNO₂ on Cr (Vl) reduction in cement. The amount of reduction is not influenced by mode of addition. In each case the first bar of a pair is the amount of Cr(VI) present in the cement and the second bar of the pair is the amount by which the Cr(V)) has been reduced in the cement.

Amount of Mode l-Added Modell-Added Cr(VI) in the directlyto to mixingwater original cement cement

Figure. 5. Effect of the mode of addition OfNaNO₂ on Cr (Vl) reduction in cement

IV. Compatibility of NaNO₂ with other admixtures for cement and concrete

Table. 1. Compatibility of NaNO₂ with one of the most powerful complex cement grinding aid -activator containing TEA and Acetic Acid among other components

*The concentration of Holcimact 1A and NaNO₂ is related to one ton of Ordinary Portland Cement Table. 2. Effect of different grinding aids on Cr (Vl) reduction by NaNO₂ from aqueous solution

*30%aq.sol **3%aq.al. *** only 15ml of each additive are added

Figure 6 shows the effect of age and temperature on the amount of Cr(VI) reduction by NaNO2. Cr(VI) reduction at 40⁰C

lnit ial Week l Week2 Week 3 Week4 CEM I A + NaN02 -B=CEM I B + NaNO2 _"■*» CEM I C + NaNO2 ~«-CEM I + NaNO2

Fig 6: Effect of age and temperature on the amount of Cr(VI) reduction by NaNO2.

V. The Reduction of Chromium Six from industrial Waste water and pH effect

Figure 7 shows the effect of pH on the amount of Cr (Vl) reduced by NaNO₂.

B Amount of Cr(VI) reduced (ppm)

Figure 7. Effect of pH on the amount of Cr (Vl) reduced by NaNO₂ (15 ml of a 30%NaNO₂ aq.sol are added to to 100 ppm Cr(VI) aq sol.)

Figure 8 shows the reduction of Cr (Vl) from aqueous solution containing different amounts of Cr(VI) (pH=5, only 15 ml added).

100 250 SOO 1000

Amount of NaNO2 added (ml 30% aq 30I )

Figure 8. Reduction of Cr (Vl) from aqueous solution containing different amounts of Cr(VI)

(pH=5, only 15 ml added)

0

o ε io iε 20

Amount NaNO2 added ( ml.30%a^ sol ) Figure 9. Rate of Cr (Vl) reduction from aqueous solution containing different amounts of Cr(VI)

(pH=5, only 15 ml added)

Figure 9 shows the rate of Cr (Vl) reduction from aqueous solution containing different amounts of Cr(VI) (pH=5). In the Figure, the first bar of each set shows the % reduction from a 100 ppm Cr(VI) aq.sol the second bar shows the % reduction from a 250 ppm Cr(VI) aq.sol, the third bar shows the % reduction from a 500 ppm Cr(VI) aq.sol, and the fourth bar shows the % reduction from a 1000 ppm Cr(VI) aq.sol.

Example 2: Use of Zn to reduce Chromium (Vl)

I. Current laboratory findings

Figure 10 shows the reduction of Cr⁶⁺ in Ordinary Portland cement by the addition of different types of Zinc salts and Zinc oxide.

Figure 10. Reduction of Cr⁶⁺ in Ordinary Portland cement by the addition of different types of Zinc salts and Zinc oxide Table 3. Rate of reduction of Cr⁶⁺ in Ordinary Portland cement by the addition of different types of Zinc salts and Zinc oxide

Figure 11 shows the reduction of Cr⁶⁺ in Ordinary Portland cement samples containing different amount of initial Cr⁶⁺ by the addition of Zinc sulfate Heptahydrate.

-CrV(l) left in cement —a— Cr(VI) amount neutralised

17.5

CEM I =control CEM I * CEM I CEM I 2%ZnSO4.7H20 [Cr(VI}=14.5ppm] - [Cr(VI)=24.5ppm] ^■ 2?£ZnSO4.7H20 2;4ZnSO4.7H20

Figure 11. Reduction of Cr⁶⁺ in Ordinary Portland cement samples containing different amount of initial Cr⁶⁺ by the addition of Zinc sulfate Heptahydrate Figure 12 shows the reduction of Cr⁶⁺ in Ordinary in Ordinary Portland cement by the addition of Zinc metallic powder and its combination with Zinc sulfate Heptahydrate.

Figure 12 Reduction of Cr⁶⁺ in Ordinary in Ordinary Portland cement by the addition of Zinc metallic powder and its combination with Zinc sulfate Heptahydrate

Table 4. Rate of Reduction of Cr⁶⁺ in Ordinary Portland cement by the addition of Zinc metallic powder and its combination with Zinc sulfate Heptahydrate.

Figure 13 shows the reduction of Cr⁶⁺ by the addition of Zinc sulfate Heptahydrate to a sample of Ordinary Portland Cement containing 5.5ppm Cr⁶⁺.

Figure 13. Reduction of Cr⁶⁺ by the addition of Zinc sulfate Heptahydrate to a sample of Ordinary Portland Cement containing 5.5ppm Cr⁶⁺

Table 5. Rate of Reduction of Cr⁶⁺ in sample of Ordinary Portland Cement by the addition of Zinc sulfate Heptahydrate

Figure 14 shows the reduction of Cr⁶⁺ in Ordinary Portland cement by the addition of a combination of Zinc sulfate Heptahydrate and Triethanolamine (TEA).

Figure 14. Reduction of Cf⁺ in Ordinary Portland cement by the addition of a combination of Zinc sulfate Heptahydrate and Triethanolamine (TEA)

Claims

1. A Cr (Vl) or Cr⁶⁺ reduction additive composition for use in cement, cement based products, mortars, concrete, waste water and mining industry waste, and in slags, which composition includes one or more chemical compounds containing the element N in the form of simple or complex anions.

2. An additive composition as claimed in claim 1 , wherein the chemical compounds containing the element N are selected from N^", N² ' N^3" , (NO₂)^", (NO₂)^2" , and (NO₂)^3" .

3. An additive composition as claimed in claim 1 or claim 2, which contains from 0.01% to 5.0% of NaNO₂ by weight.

4. An additive composition as claimed in claim 3, which when used for cementitious applications contains from 0.01% to 1.0% of NaNO₂.

5. An additive composition as claimed in any one of the preceding claims, wherein the additive composition includes one or more organic salts of Na and Ca.

6. An additive composition as claimed in claim 5, wherein the additive composition includes Ca (CH₃COO)₂, and/or CH₃COO-Na.

7. An additive composition as claimed in any one of the preceding claims, which includes in any proportions, one or more of metallic Zn, metallic Mn, metallic Fe, Metallic Mg, and metallic Sn.

8. An additive composition as claimed in any one of the preceding claims, which includes a cement grinding aid.

9. An additive composition as claimed in any one of the preceding claims, which includes one or more cement set and/or hardening accelerators based on or containing any of the chemical elements of Group IA and Group UA of the Periodic Table of Chemical Elements.

10. An additive composition as claimed in any one of the preceding claims, which includes reducing agents selected from both organic or inorganic agents including ascorbic acid or salt, oxalic acid or salt, FeSO₄, MnSO₄, SnCI₂, SnSO₄ in any crystallographic forms, Ca(CH₃COO)₂, Mg(CH₃COO)₂, Al⁰, Fe⁰, Mg⁰, Mn⁰ and Sn⁰.

11. An additive composition as claimed in any one of the preceding claims, which includes any concrete admixtures including e.g. retarders, anti-shrinkage agents, anti- washout, viscosity modifying agents, anti-alkali-silica reactions, phosphonate, lignosulphonate, polynaphthalene, polymelamine, polycarboxylate, polyacrylic, polyester, or their combinations.

12. A pre-blend, in any proportions, of any of the additive compositions as claimed in any one of the preceding claims, with any cement, slag, limestone powder, silica fume, fly ash, pozzolans, clays, dry mortar, and/or combinations thereof.

13. Use of the additive composition as claimed in any one of the preceding claims in the reduction of Cr (Vl) in waste water, soils and mining industry waste whether used in liquid or powder form, alone or in combination with other reducing agents.

14. Cr (Vl) or Cr⁶⁺ reduction and/or immobilization additive compositions for use in cement, cement based products, and in slags, which compositions include metallic Zn powder, Zn salts, and/or Zn compounds.

15. Additive compositions as claimed in claim 14, which include one or more of ZnSO₄.7H₂O, ZnSO₄-H₂O, ZnCI₂, Zn (NO₃)₂ and other inorganic Zn salts including nitride, and sulfite salts of ZN.

16. A Cr (Vl) or Cr⁶⁺ reduction additive composition for use in cement, cement based products, mortars, concrete, waste water and mining industry waste, and in slags as claimed in claim 1 , substantially as herein described and illustrated.

17. Cr (Vl) or Cr⁶⁺ reduction and/or immobilization additive compositions for use in cement, cement based products, and in slags as claimed in claim 14, substantially as herein described and illustrated.

8. A new Cr (Vl) or Cr⁶⁺ reduction and/or immobilization additive compositions forse in cement, cement based products, and in slags substantially as herein described.