The effect of anions on clay dispersion and the hydraulic conductivity (HC) of clay-sand mixtures has received little attention. This study investigates the effect that adding small amounts of anions has on the dispersivity and HC of reference clays. Mixtures of 3 and 6 g 100 g−1 kaolinite, smectite, and illite with quartz sand were packed in columns. The columns were saturated with Ca and then leached with 1 molc m−3 of one of the following organic and inorganic Na salts: chloride, hydroxide, EDTA, silicate, citrate, formate, oxalate, hexametaphosphate, orthophosphate, tartrate, or humate. Changes in HC and clay concentration in the effluent were measured and clay dispersion was evaluated as a function of the various anions added. In the kaolinite clay-sand mixtures, a significant amount of clay was observed in the effluent for all anions tested, and the HC increased above its original value. The HC of smectite clay-sand mixtures decreased following the addition of the various anions. Dispersed clay appeared in the effluent only upon addition of citrate or hexametaphosphate. In the latter two cases, the HC started to increase once maximum clay concentration appeared in the effluent. Clay concentration in the effluent of smectite was one order of magnitude lower than that of kaolinite. Illite clay-sand mixtures showed dispersion behavior intermediate between smectite and kaolinite but behaved in the same way as kaolinite with respect to HC changes.

Thermal analysis (DTA-TG-DTG), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption and mercury intrusion porosimetry techniques were used to assess the structural changes induced upon heating of two hydrotalcite-phenol (trichloro- and trinitrophenol, HT-TCP and HT-TNP) complexes, and the results were compared with those obtained for the original hydrotalcite (HT) sample. The DTA revealed thermal effects that depended on the nature of the interlayer ion in the complexes. The total weight loss (TG-DTA) increased from 37% for the original HT to 40% for HT-TCP and 77% HT-TNP, as the amount of phenol increased. The XRD and FTIR spectroscopy showed that the calcination product (550°C) of the HT-phenol complexes was indistinguishable from that formed from the original HT. Since HT-phenol complexes were prepared by phenol adsorption on calcined HT, our results confirm the recyclability of HT-like compounds as sorbents for phenols.

The present review examines the importance of dietary organic anions in preventive nutrition. Organic anions are chiefly supplied by plant foods, as partially neutralised K salts such as potassium citrate, potassium malate and, to a lesser extent, oxalate or tartrate salts. Animal products may also supply K anions, essentially as phosphate, but also as lactate as a result of fermentative or maturation processes, but these K salts have little alkalinising significance. Citrate and malate anions are absorbed in the upper digestive tract, while a substantial proportion is probably metabolised in the splanchnic area. Whatever their site of metabolism, these anions finally yield KHCO3 which is used by the kidneys to neutralise fixed acidity. This acidity essentially reflects the oxidation of excess S amino acids to sulfate ions, which is mainly related to the dietary protein level. Failure to neutralise acidity leads to low-grade metabolic acidosis, with possible long-term deleterious effects on bone Ca status and on protein status. Furthermore, low-grade acidosis is liable to affect other metabolic processes, such as peroxidation of biological structures. These metabolic disturbances could be connected with the relatively high incidence of osteoporosis and muscle-protein wasting problems observed in ageing individuals in Europe and Northern America. Providing a sufficient supply of K organic anions through fruit and vegetable intake should be recommended, fostering the actual motivational campaigns ('five (or ten) per d') already launched to promote the intake of plant foods rich in complex carbohydrates and various micronutrients.

Potassium (K) organic anion salts, such as potassium citrate or potassium malate in plant foods, may counteract low-grade metabolic acidosis induced by western diets, but little is known about the effect of other minor plant anions. Effects of K salts (chloride, citrate, galacturonate or tartrate) were thus studied on the mineral balance and digestive fermentations in groups of 6-week-old rats adapted to an acidogenic/5 % inulin diet. In all diet groups, substantial amounts of lactate and succinate were present in the caecum, besides SCFA. SCFA were poorly affected by K salts conditions. The KCl-supplemented diet elicited an accumulation of lactate in the caecum; whereas the lactate caecal pool was low in rats fed the potassium tartrate-supplemented (K TAR) diet. A fraction of tartrate (around 50 %) was recovered in urine of rats fed the K TAR diet. Potassium citrate and potassium galacturonate diets exerted a marked alkalinizing effect on urine pH and promoted a notable citraturia (around 0·5 μmol/24 h). All the K organic anion salts counteracted Ca and Mg hyperexcretion in urine, especially potassium tartrate as to magnesuria. The present findings indicate that K salts of unabsorbed organic anions exert alkalinizing effects when metabolizable in the large intestine, even if K and finally available anions (likely SCFA) are not simultaneously bioavailable. Whether this observation is also relevant for a fraction of SCFA arising from dietary fibre breakdown (which represents the major organic anions absorbed in the digestive tract in man) deserves further investigation.