Powders and granules and process for making such powders and granules

A process for making a powder or granule comprising at least one chelating agent selected from the group consisting of an alkali metal salt of methyl glycine diacetic acid (MGDA), an alkali metal salt of glutamic acid diacetate (GLDA), and an alkali metal salt of iminodisuccinic acid (IDS), wherein the alkali metal salt has a formula selected from the group consisting of formula (I a), (I b) and (I c):

• [CH3—CH(COO)—N(CH2—COO)2]M3-xHx (I a)
• wherein in formula (I a), M is, independently at each occurrence, an alkali metal cation, and x is from zero to 1.0,
• [OOC—CH2CH2C—CH(COO)—N(CH2—COO)2]M4-xHx (I b)
• wherein in formula (I b), M is, independently at each occurrence, an alkali metal cation, and x is from zero to 2.0,
• [H—N—(CH(COO)—CH2COO)2]M4-xHx (I c)
• wherein in formula (I c), M is, independently at each occurrence, an alkali metal cation, and x is from zero to 2.0,
• the process comprising:
• (a) introducing an aqueous solution or aqueous slurry of the chelating agent into a spray-dryer or spray-granulator, and removing most of the water by spray-drying or spray granulation using a gas with an inlet temperature of 125 to 250° C.,
• (b) withdrawing powder or granules, from the spray-dryer or spray-granulator,
• (c) separating off fines from the powder or granules, wherein the fines have a maximum particle diameter of 30 μm in the case of powders and a maximum particle diameter of 350 μm in the case of granules,
• (d) separating off lumps from the powder or granules, wherein the lumps have a particle diameter of 250 μm in the case of powders and 1,000 μm or more in the case of granules, respectively,
• (e) milling the lumps to a maximum particle diameter of 500 μm in the case of granules or to 40 μm in the case of powders, and
• (f) re-introducing the fines from (c) and milled lumps from (e) into the spray-dryer or spray-granulator,
• wherein the amount of fines is in a range of from 4 to 18% by total weight of the chelating agent withdrawn in (b), and the amount of milled lumps from (e) is in a range of from 20 to 40% by total weight of the chelating agent withdrawn in (b).