Journal of Applied Sciences and Environmental Management World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt ISSN: 1119-8362 Vol. 11, Num. 4, 2007, pp. 67-69

Journal of Applied Sciences and Environmental Management, Vol. 11, No. 4, 2007, pp. 67-69

Studies on the effect of temperature on the sedimentation of insoluble metal carbonates

¹*VICTOR N. MKPENIE; ¹GODDY EBONG; ²BEAUTY ABASIEKONG

¹Department of Chemistry, University of Uyo, P. M. B. 1017, Uyo, Nigeria.
¹Department of Science Technology, Akwa Ibom State Polytechnic, Ikot Osurua, P. M. B. 1200, Ikot Ekpene, Nigeria.
*Correspondence: Fax: (+234) 803 175080179; Tel: (+234) 803 5080179; email: vicmkpenie2@yahoo.com
* Corresponding author: Victor N. Mkpenie; email: vicmkpenie2@yahoo.com

Code Number: ja07097

ABSTRACT:

The effect of temperature on the sedimentation rate of some insoluble metal carbonates has been investigated in this work. The sedimentation constants show that a 20°C rise in temperature typically doubles the rate of sedimentation. Cadmium carbonates have higher sedimentation constants while nickel had the lowest sedimentation constants. The order of sedimentation does not seem to have any dependence on temperature. The minimum energy needed to activate the sedimentation process was higher for Zn²⁺, 67.90kJmol-1 and lowest for Ni²⁺, 25.5kJmol^-1. The dependence of the metal carbonates on temperature follows the order Zn²⁺> Cd²⁺>Cu²⁺> Co²⁺> Ni²⁺.

Sedimentation is the settling out of solid particles (sediments) in a liquid by gravity (Atkin, 1994). Chemical sediments represent precipitation of materials in solution either by simple chemical precipitation or by the activity of organisms (Fisher, 1997). Sedimentation readily occurs when particle size is above 1000nm. Particles below 1000nm exist as colloids in solution (Shaw, 1992). There are many chemical reactions that form solid deposits (precipitates). Precipitation is the process that produces a separable solid phase within a liquid medium (Vemulapalli, 1993). The free settling of the precipitates under gravity can be monitored to determine sedimentation rates, sedimentation constants and sedimentation orders of the insoluble compounds. These parameters have been determined for the insoluble transition metal hydroxides (Essien, 1992) and cobalt(II) insoluble compounds (Essien and Ekpe, 1998). Sedimentation studies have been used to determine the molecular weights of protein (Lustig et al, 2000).

In continuation of our work on sedimentation (Mkpenie and Onwu, 2006), we examine the effects of temperature on the sedimentation of insoluble transition metal carbonates. This study may provide models for correction of temperature variation on sedimentation parameters.

EXPERIMENTAL

All chemicals used were of analytical grade.

Procedure

The experimental procedure was similar to the one used elsewhere (Mkpenie and Onwu, 2006). 20 ml of the precipitating agents (0.1M Na2CO3) was gently added to 20ml of the metal ions (0.01-0.2 M) in a 100 ml measuring cylinder, stirred and allowed to stand. The time taken for the precipitates to fall was recorded at various volumes along the measuring cylinder. This was carried out at different temperatures, 8°C, 21°C, 28°C and 50°C. The rate of sedimentation was obtained from the slope of the plot of the change in volume of the sedimenting carbonates (?V) against time (t). The precipitated carbonates were obtained as expressed in equation (1) and the rate of sedimentation was obtained according to equation (2).

where

R_S is the sedimentation rate
k_S is the sedimentation rate constants = k/[A]^b
[Mⁿ⁺] is the concentration of the metal ion

a and b are sedimentation orders

The sedimentation constant kS was deduced from the intercept of the plot of log RS versus log [Mⁿ⁺] while the sedimentation order was deduced from the slope. The variation of sedimentation with temperature was determined by Arrhenius plot, InkS versus 1/T.

RESULTS AND DISCUSSION

The sedimentation rates of some transition metal carbonates were determined under the influence of gravity. Variation of sedimentation parameters with temperature is shown in table 1. The rate of sedimentation has been found to follow Arrhenius equation as in chemical reactions. Zn²⁺ has higher sedimentation rates while nickel has lower sedimentation rates. The rates at all temperatures seem to follow the order Zn²⁺> Cd²⁺> Cu²⁺> Co²⁺> Ni²⁺. The sedimentation order shows no dependence on temperature. Ni2+ has second order of sedimentation, Zn²⁺ and Co²⁺ have first order while that of Cu²⁺ and Cd²⁺may be 3/2 and 1/2 respectively.

Arrhenius equation predicts that a small increase in temperature will produce a marked increase in the magnitude of the rate constants. The rate of sedimentation typically doubles for a 20°C rise in temperature. At higher temperatures (>50°C), sedimentation becomes difficult. This is due to increase in solubility of the carbonates.

The sedimentation activation energy for Zn2+ was higher (67.9kJmol^-1) while that of Ni²⁺ was lower. (25.5kJmol^-1). This may represent the minimum energy required for sedimentation to occur and may involve mostly the energy of interaction of the precipitates with the liquid medium. Reactions with small activation energy (about 10kJmol^-1) have rates that increase only slightly with temperature whereas reactions with large activation energy (about 60kJmol^-1) have rates that depend strongly on temperature (Atkins, 1989) (Figure 1). Thus, sedimentation rates in Zn2+ depends strongly on temperature. The dependence of metal carbonates on temperature follows the order: Zn²⁺> Cd²⁺>Cu²⁺> Co2+ > Ni²⁺.

In conclusion, sedimentation, being a physical phenomenon has shown much resemblance to chemical processes and follows Arrhenius-type behaviour. There is a general increase in the rate of sedimentation with temperature. A 20°C rise in temperature typically doubles the rate of sedimentation. The order of sedimentation is independent of temperature.

• REFERENCES
• Atkins, P W (1989). General Chemistry, Scientific American Book, USA.
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• Fisher, A G (1997). Sedimentary rock. In: Parker S P (ed.) McGraw Hill Encyclopedia of Science and Technology 8th ed. Vol. 6, McGraw Hill Inc, USA, p 194.
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• Essien, I O ; Ekpe, S D (1998). Determination of sedimentation rates of cobalt(II) insoluble compounds and absorption coefficient of the sedimenting particles using gamma radiation. J Chem Soc Park 20: 120-124.
• Lustig, A; Engel, A; Tsiotis, G; Landau, E M; Baschong, W (2000). Molecular weight determination of membrane protein by sedimentation equilibrium at the sucrose and mycodenz-adjusted density of the hydrated detergent micelle. Biochim Biophys Acta Biomembrane 1464(2): 199-206.
• Mkpenie, V N; Onwu, F K (2006). Determination of sedimentation rates and absorbtion coefficient of insoluble metal carbonates. J Appl Sci Environ Mgt 10: 123-126.
• Shaw, D J (1992). Introduction to Colloids and Surface Chemistry, 4th ed. Butterworth-Heinemann Ltd, Jordan.
• Vemulapalli, G K (1993). Physical Chemistry, Prentice-Hall Inc, England.

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