$(function () {
 
    var processed_json = new Array();
    $.getJSON('abitschart', function (data) {
 
        for (i = 0;i < data.abiturients_data.length;i++) {
            processed_json.push([data.abiturients_data[i].key, parseInt(data.abiturients_data[i].value)]);
        }
        $('#chart').highcharts( {
            chart :  {
                type : "bar"
            },
            title :  {
                text : "Abiturients data"
            },
            xAxis :  {
                categories : ['KT(AB)', 'KT(TIE)', 'IQ', 'MN', 'BHA', 'EE', 'YeUTT', 'ET, EM', 'AB', 'AT', 'MKQ', 'TIE', 'TK', 'BIQ', 'Servis', 'Logistika'], 
                title :  {
                    text : null
                }
            },
            yAxis :  {
                title :  {
                    text : "Number of abiturients", align : 'high'
                },
                lables : 'justify'
            },
            tooltip :  {
                valueSuffix : ' ta'
            },
            credits :  {
                enabled : false
            },
            series : [{name : 'Abiturients', data : processed_json}]
        });
    });
});

var keys_json = new Array();
for (i = 0;i < data.abiturients_data.length;i++) {
            keys_json.push([data.abiturients_data[i].key]);
        }
....
categories : [{data:keys_json}]