Salt sensor in aqueous solution (35-42g / l)

Hello Arduiners.
I was wondering if :

  • the salt sensor which can be connected to a board (Arduino board for example) exists.
    If yes, can you tell me where can I find it?
  • a mini pump that can be controlled from a card exists.
    If yes, can you tell me where can I find it?
    I want to recreate a mini desalination station.

That is sea water, right?

You need an EC sensor for this. There are such sensors that claim 6 orders of magnitude which I've seen for sale at about USD 100 a piece (reportedly can be found for about USD 20 a piece); I have achieved 5 orders of magnitude with a 555 based circuit (basically tap water to sea water) and simple EC probe, pretty cheap overall.

The biggest problem is the really high conductivity of sea water, the 555 can't deliver enough current so needed a few buffers in parallel to get sufficient current. Come to think of it, maybe a MOSFET gate driver can help me in this project... If you're in for some serious building let me know.

You don't need high current to measure low conductivity, you can simply have a more sensitive
voltage sensing.

If AC current is used you eliminate DC offset errors due to electrochemical potentials and its
easier to amplify small voltages accurately. Also it reduces any electrolysis at the electrodes
by reversing the reactions immediately. A 4-wire connection to the electrodes might be needed
for very high conductivities to eliminate wiring resistance.

Another approach is to use a fixed voltage, but only in brief pulses, and measure the current.
The voltage can be arranged to dwarf electrochemical potentials, and the pulses short to reduce
the amount of electrolysis.

In any method using inert electrodes is good, carbon has rather high resistance alas, and platinum is
expensive, but stainless steel is a reasonable compromise (ie will electrolyze, but not corrode when
not active).

My method revolves around measuring the discharge time of a small capacitor. In seawater that results in currents of ~50 mA.

It's a serious project.
It's in the state of a theoretical project not completed.

There are different types of desalinization possible and I have not yet considered (I don't t know what prices to invest in sensors, but there are expensive!) -> Can we create it ? or is-it too complex?
What are the simplest sensors to use on an Arduino board? (with a real-time display for example)

The objective is to have an autonomous system where an outside intervention in case of problems is possible. (for example, too early high salt in the tank of pure water at the end of the loop)
Mini pumps don't seem to exist, can we easily create these? Another solution would be to make a staircase system with a movement of water by gravity (however this system will not allow doing an autonomous cycle since the desalinated water will remain at the bottom of the system)

I thought to run the pumps and sensors by simple batteries (batteries)? Is it powerful enough?

thx for reading and responding.

None of your questions can be answered without a lot more information.

What range of salinity do you need to measure?
How will the water be desalinated?
What volume of water will be desalinated per unit time?

You will need practical experience in order to decide what you want. I suggest to start doing some small scale experiments.

EC sensors can be built pretty cheaply, especially the low salinity (output) part is easy. All you need for this is a probe with two pins (stainless steel is great), two resistors and three capacitors. This I'd say is the most important of the two, as you don't want too much salt in your drinking water.

The high salinity part is a bit harder, but can also be done without high expense. It's less important: just pump enough sea water through your system and you don't see much increase in salt concentration.